Science topic

Heterogeneous Catalysis - Science topic

In chemistry, heterogeneous catalysis refers to the form of catalysis where the phase of the catalyst differs from that of the reactants. Phase here refers not only to solid, liquid, vs gas, but also immiscible liquids, e.g. oil and water. The great majority of practical heterogeneous catalysts are solids and the great majority of reactants are gases or liquids.
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I am confused between the meaning of loaded and supported catalysts. Are these two terms same or different?
Please clarify my doubt.
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If feed gas flow rate is 50 cc/min how can i calculate.
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Zakia Akter Sonia, Just divide the gas flow rate by the catalyst volume, here in cc, and multiply by 60 to refer to one hour.
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Heterogeneous catalysts (CaO, MgO, ZnO) have been shown to be less effective in low methanol and oil mole ratios. So, what is the best mole ratio for a heterogeneous catalyst in transesterification?
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For CaO catalyst the best methanol/oil ratio is 12 (molar ratio).
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I am doing experiments about oxidation process from limonene to limonene glycol, but the product are some limonene oxide (which I don’t want). These are the chemicals I have:
-Catalyst: CuY (zeolite Y supported by Copper); Cu/Fe spinel mixture.
- Solvent: dimethyl formanmit.
- TBHP and H2O2
- Method: Use reflux condense.
Can you give me some condition to improve the process (other chemicals, temperature, time…)?
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I think if you use H2O2 35 % the water is sufficient to form diol, to increase the formation of diol you can realize the reaction in presence of acid, for example a solid acid like NAFION, more easy to remove after the reaction
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I oxidize limonene in a 3-neck round flask, the main neck is connected to the condenser, I heat the limonene, catalyst (CuY or CuO/Y) at 60-70 Celsius Degree for 4, 6, 8, 10 hours. All of the samples (gas chromatography method) show high conversion rate but really low selectivity. Can anyone tell me how to increase it?
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I will try it and see the result. Thank you, Mr. Yurii V Geletii
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I oxidize limonene in a 3-neck round flask, the main neck is connected to the condenser, I heat the limonene, catalyst (CuY or CuO/Y) at 60-70 Celsius Degree for 4, 6, 8, 10 hours. All of the samples (gas chromatography method) show high conversion rate but really low selectivity. Can anyone tell me how to increase it?
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Hi, Tran Khanh,
To increase the selectivity of limonene oxidation, is it possible for you to protect, before, the endocyclic double bond?
Safia
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I am currently working with an experiment producing biodiesel from a heterogeneous catalyst. After the reaction I have to recover the catalyst after the reaction is over. I hope to use the centrifugal method to bind the catalyst to the surface of the centrifugal tube as a Pellet. However, I can not take the bound catalyst superficially.
How i can recovered this heterogeneous catalyst?
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After the last reaction analysis is complete. Dilute it with methanol and wash it, centrifuge again, the catalyst will be better recovered.
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In transesterification some of heterogeneous catalyst such as BaO, SrO, MgO, and CaO shows different biodiesel yields. In general, BaO and SrO show high activity than MgO and CaO. My question is how these compounds do have different catalytic activity?
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Dear Viraj Miyuranga . See the following useful link: http://www.bioline.org.br/pdf?st11020
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Actually I have prepared Al-VPO. But I did not get any peak of Al in the XRD pattern of Al-VPO. So it might be well dispersed or amorphous? If so then which is the active sites if I'll use it for any oxidation reaction?
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XRD should show peaks for crystalline and amorphous phases as well. Loading may be low and not as reported (5%).
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Can anybody share a comprehensive study on the comparison of light sources (lamp name with power value, manufacturing company, and associated wavelength range) with that of photocatalytic performance. However, sharing the comparison with sunlight is highly encouraged.
Sharing of general opinions by field researchers are warmly welcomed, positively.
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Dear Iqrash,
There are many, many options. Personally, I recommend high pressure Xe arc lamps. They are not cheap, but they simulate the solar spectrum well. Of course, it will depend on the application to be done and the budget, but this is a good option. Eventually, for visible radiation only, conventional lighting LED lamps can be used, which also work well and are very cheap. You can see the first ones (high pressure Xe arc lamps) in the following link:
Best,
Fran
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I have been convinced by the concept of direct desulfurization of crudes. The commercial development in this technology will help ridding off the require the of mutilpe reactors with different ranges of Catalytic beds in the modern petroleum refinery.
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Ahh Bugs replacing refinery process again. A 50+ year old dream that will probably come true some day - but probably not in my lifetime.
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Dear Scientists,
Hoping all you are fine.
I need to know if someone can recommend me how to know if Al extracted from a zeolite is extraframework or of the framework? (Other technique than NMR of Al)
In Colombia it is complicated to perform NMR of solids and we need to know that data.
Open also to collaborations.
Thanks a lot,
With kind regards,
Julián Sánchez.
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Thanks al, for the response please help me I need Complication Neonatal framework
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Could TOF be affected by any catalyst properties or reactor conditions? Please share more light on the choice of your answer (other than Yes/No) and if possible provide supporting materials. Thank you all.
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Thank you Sina Safavi
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I am currently trying on a synthesis involving Amberlyst-15 (polystyrene with sulfonic group at p-position) as a proton donor. When following the reaction process by quantitative 1H NMR, I am noticing that part of my (basic) reactant (2-methylimidazole) is being immobilised against the resin and is unavailable for reaction with the rest of the reactants.
Has anyone experienced this when working with similar ion excange resins?
I am trying to figure out ways to liberate it from the resin. Any suggestions would be greatly appreciated.
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Dear Trey Todor Koev thanks for sharing this very interesting technical problem with the RG community. I'm absolutely no specialist in this field, so perhaps my thoughts are a bit naive. I assume that you just have an acid-base reaction in which the 2-methylimidazole formed a tightly bound sulfonate salt with the ion-exchange resin. In this context, please have a look at the following potentially useful article which might help you in your analysis:
Anchoring a Co/2-methylimidazole complex on ion-exchange resin and its transformation to Co/N-doped carbon as an electrocatalyst for the ORR
Unfortunately this paper is not freely available as public full text on RG. However, all ten authors have RG profiles, so that it should be no problem to request the full text of the paper dierctly from one of the authors via RG.
Good luck with your work!
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I am trying to impregnate 10wt%Cu-10 wt%Fe on alumina pellets (1/8" in diameter, Alfa Aesar). The procedure I am following right now is mixing the alumina pellets and metal nitrate solutions (copper nitrate and iron (III) nitrate) with a weight of support to the volume of deionised water ratio of 1:5. The solution+support is mixed using a rotavapor for 3 hours and then the pellets are filtered out . Obviously, the filtration method will not ensure the required Cu-Fe loading on the alumina pellets. The problem is that when I mix and rotate the solution+pellets, the color of the solution changes from green to brown (I suspect some reaction of alumina with the metal nitrates). I tried to evaporating the metal precursor solution after impregnation using the rotavapor at 60°C of the water bath temperature (instead of the filtration step), but it led to the deposition of brown residue on the alumina pellets. What suggestions you will have to have an effective impregnation?
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Based on my experience, when Cu is introduced by the wet impregnation, the solvent elimination using filtration is not sufficient for some supports. However, the rotary evaporator might be used instead. I have also observed the change in color, however, it did not affect the properties of the calcined catalyst.
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I am looking to find a material (any type) that can offer me CO formation energy (> 2.0 eV) and NO formation energy ( < 0.5 eV) simultaneously. Secondly, how to confirm these formation energies experimentally? Your expert opinion in surface reaction, catalysis would be appreciated. Thanks
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Thank you Professor Frank T. Edelmann for the great insight. sure, I'll go through the mention linked. well, from your expertise, will you please suggest some potential materials which can show desired chemistry. Thanks
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In the case of water splitting the water oxidation (OER) is the bottleneck for the process and because of the harsh conditions of the WO reaction, molecular catalysts with high TOFs are not stable in the matrix and quickly decompose. On the other hand heterogeneous catalysts are more stable but they often do not have high TOF quantities. Now what is your opinion about the future catalyst type? Will the ideal catalysts fabricated by turning the molecular catalysts to heterogeneous catalysts ( by loading the molecular catalysts on the solid surfaces ) or it will be from the single atom heterogeneous catalyst type?
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Dear Sina Safavi thank you for initiating this interesting RG discussion. Although we are inorganic chemists, I'm not an expert in this field. However, I agree with Yurii V Geletii in that there is no such thing as a true catalyst. In this context I suggest that you have a look at the following relevant article which has been published Open Access. It is stated there that future catalysts should be "low-cost and earth-abundant":
Earth-Abundant Electrocatalysts for Water Splitting: Current and Future Directions
(see attached pdf file)
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Influence of ligand on an heterogeneous catalyst surface reactivity
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Thank you for sharing idea Madhukar Baburao Deshmukh
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I wonder which one is more important in means of catalyst design: Number of active sites or TOF value. TOF value already considers number of active sites but the challenging part seems to determine the active sites. Computational methods calculate TOF value without considering number of active sites and experimental methods have different approaches to estimate TOF value, in most of the papers I can not even see the estimation of number of active sites but an ambigious TOF value. If we talk about the catalyst activity TOF value is the measure but if we talk about the catalyst design, shouldn't it be the real textural properties and consequently the number of active sites?
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Dear Ebru Erunal you are asking an interesting question. Here's what we do when calculating TOFs for heterogeneous catalysts:
1. We start from its definition:
TOF = rate of reaction/concentration of active sites [=] [(mol reactant/s)/(mol active sites)] = [1/s]. Therefore, as it name implies, TOF is a frequency whose units are Hertz.
2. We consider that the rate of reaction that must be used to calculate TOF must be the intrinsic rate of reaction of the catalytic sites. Therefore, the following conditions must be fulfilled: (i) no transport limitations (mass and temperature gradients) must be present, (ii) as the reaction rate is a function of the advancement of the reaction, the intrinsic rate of the active sites must be as far from full conversion or equilibrium conditions as possible. For this, the rate should be extrapolated to zero conversion and free of the inhibition effects that products may have on the catalytic process. In a fixed-bed reactor, this means that the reactor should be operated in a differential mode; i.e. the conversion should be as close to 0 as experimentally feasible. Also, tests feeding products must also be done. In a batch reactor, this means that the initial rate of reaction is the most suitable for the calculation. For calculating the latter, samples must be taken as close to zero time as possible.
3. Measuring the concentration of active sites may be the most difficult part since one must answer the question: what is the active site for the reaction that you are investigating. Typically, you have the following possibilities: (i) for catalysts based on metallic nanoparticles (supported or not) where the latter are responsible for activating the most stable reactant (e.g. in methane oxidation, methane is hardest to activate than the oxidation agent -O2 or H2O, etc-), the number of moles exposed at the surface of the catalyst is well accepted as a metric for estimating the number of active sites. As you may know, this can be measured by chemisorption of some adequate probe; e.g. H2, CO, etc. (ii) for catalysts based on (supported or unsupported) oxides, sulfides or nitrides, the active site is also normally associated to an exposed metallic center or to a given structural site. Therefore, certain assumptions are always before defining a metric for the concentration of active sites. As an example, MoS2 catalysts have sites located in different parts of its geometrical structure and the specific role of these different sites depends on several factors associated with the type of molecule that is reacting, the reaction conditions, the possible interconversion of sites, among others. (iii) for bimetallic catalysts, e.g. Pd-Pt, one would need to define the specific role of each metal in the reaction. It may be the case that both metals are active in the reaction or that only one of them is. Therefore, as in the case of (ii) certain assumptions about the nature of the active sites -and reaction mechanism- must be made. (iv) For bifunctional catalysts; i.e. those where the support also contributes active sites, one should take into account the same as in (i).
Well, the points above are our rough guide for calculating TOFs. We have got help from literature such as the few ones cited below:
1. Foggler's Elements of Chemical Reaction Engineering
2. Chorkendorff and Niemantsverdriet's Concepts of Modern Catalysis and Kinetics
3. Froment and De Wilde's Chemical Reactor Analysis and Design
4. Harris et al. Consequences of product inhibition in the quantification of kinetic parameters, Journal of Catalysis 389 (2020) 468–475
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Any significant progress in the design or innovation of solid catalyst for biomass hydrolysis and sugar fermentation into alcohols in a biorefinery? If yes, I would like to have some recent updates regarding that subject. Thank you all
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Thank you for your answer,
Pedro Nakasu
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Could the presence of ligand on a catalyst surface reduced the reactivity of its surface? If yes/no, please explain why?
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this depends on which type of ligand used
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Dear all
I have calculated the d-band centers (proposed by Norskov and others in chapter 8 of the book "Fundamental Concepts in Heterogeneous Catalysis". My system is a spin polarised system.
Can I safely say, total DBC (d-band center) = DBC_up + DBC_down
and similarly
d-band width = d-band width_up + d-band width_down
I greatly appreciate your response. Thank you.
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I meet the same problem. Have you worked it out?
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When there is the Thiele modulus and the effectiveness factor to determine the pore resistance in catalysts, why do we need the Wagner modulus?
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Wagner model is a rheological model developed for the prediction of the visco-elastic properties of polymers
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I would like to know the difference between the turn over frequency, rate of the reaction and the activity of the catalyst?
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(TON) number of moles of reactant consumed/(mole of catalyst TON/time of reaction.
Turnover frequency (TOF) = Turnover number/ time of reaction. Hence , TOF indicates the activity of a catalytic centre for the reaction
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We have online GC-FID and GC-TCD (Mod: 2014) connected with flow reactor system.
This GC-FID/TCD is connected to a gas line coming from flow reactor system which I used for cascade reaction. In this flow reactor system ethanol is pumped with constant rate & heated at 160 oC and an inert gas (flow controlled by MFC) is using as carrier gas for ethanol. To prevent from condensation of ethanol, the line is wrapped with heating tapes. Further, the gas/ethanol flow through a loop in the GC-FID and GC-TCD, and when the sampling process starts, the GC takes the gas in the loop to column by pressing the switch (activate sampling at same time).
In this system, I flow the gas/ethanol at constant conditions in flow reactor for the long time as well, but I get instable peak area of ethanol in GC-FID as depicted in attached figure.
I tried a lot by changing the flow reactor parameters, checked gas leak, pressure regulators, sampling time. but facing the same problems.
Could anyone suggest me, where is the problem or anyone facing such type of issues?
Thanks in advance
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Raju Kumar , what is the initial temperature of the oven ?
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Heterogeneous Reactions: Analysis, Examples and Reactor Design: Gas-Solid and Solid-Solid Reactions L.K Doraiswamy and M.M Sharma
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Hi
I have this book. If you need send me an email yo Aimanr@yahoo.com
Adiabatic Fixed-Bed Reactors: Practical Guides in Chemical Engineering
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Both these phenomena are termed catalysis, but clear and complete discussion and specification of their similar and distinguishing features would be useful.
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Heterogeneous catalysis the phase of catalysts differs from that of the reactants or products. On the other hand homogeneous catalysis the catalyst is soluble forms a homogeneous mixture with the reactants . The common feature in both types of reactions reaction occurs at the surface .The rate depends upon the amount of the reactants and nature of the substrate. Sterically crowded substrates may undergo the reactions less readily in both the cases.
and products and ... the surface.
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I want to model a reaction between solid state catalysts of a core-shell system for example Fe3O4@MnO2 and an alcohol for example benzyl alcohol. In this case I want to determine the activity of the reaction. Also I want to determine the reaction rate and re usability of the catalysts. Anyone with ideas on this kind of study and the appropriate software can help please.  
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I agree with ulián E. Sánchez
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I'm looking for an enzyme with reduced size for covalent immobilization onto a mesoporous catalyst (pore size around 7-8nm). Up to now I have used glucose oxidase (GOD, E.C.1.1.3.4) whose volume is 6.0 x 5.2 x 7.7 nm3 (see attached reference), without any promising results. Does a "smaller" enzyme (ideally monomeric) of this type exist? Is it available from purchasers?
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Deglycosylated enzymes in which the sugar has entirely removed, especially from a glycoprotein, should be a good choice for your immobilization method.
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Hi,
I have impregnated my activated carbons with a solution of PEI (Polyethyleneimine) using either methanol or water as solvent.
I was wondering how I could work out the amount of polymer which has been actually loaded onto my carbons after carrying out the wet impregnation procedure.
I've been recommended to use a gravimetric method (i.e. mass balance). However, in order to have a reliable figure, I'd need to make sure to completely remove the solvent (methanol or water) without losing any polymer. Could you suggest any suitable drying conditions in order to achieve that?
Also, could you recommend any alternative method? For instance in some papers authors performed TGA for impregnated and virgin carbons and worked out the actual PEI loading as difference in their volatiles content (assuming that the excess of volatiles in the impregnated sample is due to the polymer decomposition). Which type of temperature programme could I use in this case?
Thanks,
Antonio
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You can remove most of the moisture by freeze drying.
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I know the Cuprous ion loses an electron during the CuAAC reaction. Resulting in formation of more stable in aqueous solutions cupric ion. I also observed that all triazoles obtained in homogeneous conditions are contaminated by copper, up to 168 ug/100mg of product. Cupric ion is most likely coordinated to the two nitrogen lone pairs on the triazole ring. If I was to avoid contamination. Should I chose a heterogeneous catalysis or is there a method that allows to remove the copper form from the already contaminated triazole product?
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interesting question
Following the answers
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Whenever I pyrolyzed NaH2PO2, I am facing difficulties in cleaning the left over white residue (may be phosphates) in the tube.
So, I am looking for any effective cleaning protocols to get rid of this issue.
Thanks.
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Yes Mr.
Curtis Guild
Actually, when we try for the annealing of potassium niobate, we suffer from those cracks on the tube. The niobium gets reacted with Si and forms Niobium Silicate. Those cracks are at inner surface of the tube. And cracks get propagated and unfortunately that tube get damaged.
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Hello dear scientists,
I carried out an adsorption-desorption isotherm of a catalyst as show in the attached file. Nevertheless, when I was analyzing the desorption I observed that this way is so strange since this isotherm present a mix between H2 and H3 loop.
I don't know why is the reason?
I repeated the experiment but I obtained the same isotherm.
Could some one explain me why could be the reason of the desorption way?
Thanks a lot,
Julián.
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Julián E. Sánchez-Velandia The isotherm is a beautiful example of pore blocking and a desorption step referred to as "cavitation". The isotherm has blended hysteresis characteristics of H2(a), H2(b) and H3/H4 !!
The large cavitation step is due to a significant volume of mesopores (given by the step height) which are blocked by micropores. These papers will explain in more detail exactly what is cavitation:
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I am setting up process flow scheme where multiple CSTR's in series are being utilized for heterogeneous catalysis. Catalyst (solid) plays vital role in reaction hence it is necessary that catalyst is not lost along with product stream from CSTR.
How can I stop the catalyst going out with product stream so that uniform catalyst distribution is maintained in each reactor.
Please help.
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Both types of reactors (Carberry and trickle-bed) allow to react continuously the feedstock and recover the fluid phase at the exit of the system but maintaining the catalyst inside the reactor. Don't need a filtration system outside the reactor. However it'll be advisable an elemental analysis of the líquid phase at the exit of the reactor since in some liquid-phase reactions the catalyst leaches towards the liquid, It depends on the nature of the catalyst and reactant.
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Hello, dear Scientists
I would like to know why in some cases, if you impregnate metal in a support (in different percentages, e.g.: 1%, 2%, 4%) the surface area of the final material do not change significantly.
What could be the reason of this fact?
Maybe the same dispersion and for instance the same crystal size??
Thank you so much,
With kind regards,
Julián E. Sánchez.
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The surface area depends on the dimensions thus if the doping material has comparable size or ( radii) you may get similar surface area.
It is depend on how did you calculate the surface area? I suggest you to run the BET to get the accurate value of the surface area.
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Hello dear Scientists,
I would like to ask to everyone about a technical aspect in the preparation of catalysts using incipient wetness impregnation.
¿Can change drastically the properties of the material if I do not use atmosphere of nitrogen in the impregnation of metal over a support?
Always it is necessary the use of nitrogen or other inert atmosphere during impregnation of the metal?
Thanks a lot for your answer,
With kind regards,
Julián Sánchez.
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The metal content in the impregnation method is usually insignificant (2-5%w), also due to the low solubility of the atmospheric gases in the impregnation solvents (H2O, EtOH, ...) it can be say the atmosphere effects on impregnation are negligible.
use of ultrasonic method, surfactant assisted method and calcination condition (temperature and atmosphere) are more important parameters for enhancing of metal dispersion on supports.
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I have passivated my catalyst to prevent oxidation; now before promotter addition, I would like to know the temperature to re-reduce the catalyst. That can be presicted by TPR. For the latter, the maximum temperature to reach depends on the thermal stability of the catalyst, hence TGA is beleived to satisfy this aim. I would to know more information that can be derived from such results or if once come accross a similar project.
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Besides the thermal stability, you can calculate the activated energy, the mass ratio between the combustible and incombustible fractions, and integral procedural decomposition temperature (IPDT).
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reduce Graphene oxide supported metal nanoparticles
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If there is a COOH group on the surface, then you add one equivalent of hydroxide Me (OH) 3. It reacts with the carboxyl group. Then you heat it up to remove water from the acid salt. You get oxide on the surface of GO.
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I wonder if there is a simple methodology (apart from the Gibbs Phases Rule or visual inspection) to determine the number of liquid phases in a given mixture. Any suggestion will be very appreciatted and helpful.
All the best,
Carlos
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hello,
you can separate the mixture to enhance the phase rule is F= C-P+2 or F=C-P+1 or F= C-P......
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Recently, I was synthesized Zeolites Y with the mix of Ludox and NaAlO3. Is there any literature or good tip for me to modify Zeolites Y into Ultra-stable Zeolite Y? best regards.
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Yes, Halima, but the question was how po prepare Ultrastable zeolite Y. For the increase the stability of Y-zeolite to the level "Ultrastable" its structure must be quite strongly dealuminated, by wery low acid concentration it can be prepared only H-form of Y-zeolite with very small dealumination, and, as you mentioned, it is necessary to calcine it very carefully to keep the crystallinity. Ultrastable Y-zeolite must by prepared by hydrothermal treatment at the temperatures above 500 °C - at this condition a hydrolysis of framework aluminumum occurs creating extra-framework Al-species (EFAL), and Al-vacancies in framework are partially replaced by Si-atoms. Then, EFAL species could be partially extracted by mineral acid - its concentration can be even higher, because after hydrothermal dealumination in e.g. deep-bed conditions at 550-750 °C the dealuminated structure of USY is strong enough to be stable against acid treatment. There are also another methods how to dealuminate the structure of Y-zeolite - slow extraction by H4EDTA-acid, but the hydrothermal steaming is the most used method for the prepartation of Ultrastable Y-zeolite. Method you propose is suitable for H-form of Y-zeolite preparation, but without higher stability.
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I am preparing a heterogeneous adsorbent for heavy metal removal. the main active group was the carboxylic group. during preparation, the catalyst was treated with aqueous sodium hydroxide for a long time (24 Hr). sodium carboxylate formation was confirmed. my question is how to obtain the carboxylic group free again. ideas, detailed procedures, and similar paper are highly appreciated.
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I understand/guess your material is a sort of an ion-exchange resin in its Na+ form. You have been rightly suggested to treat that with dilute HCl solution.
Depending upon the quantity, you may take your material in a column of appropriate dimension (diameter and length) and then charge the column with dilute HCl from top. Monitor the pH of the liquid coming out of the column from its bottom. Completion of exchange should be indicated by acidity of the out-going solution from the bottom of the column.
With best wishes,
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Anyone having experience of NH3-TPD analysis with activated carbon?
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Dear Riikka
Please go through Shah et al. 2015 (Mater Sci Engg B). I do hope you can get some help.
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Professor Taufiq-Yap Yun Hin
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yes its seems correct@Peter Alaba
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Hi dear Scientists! :)
I was impregnating Fe or Cu over different mesoporous materials, and after TPDA analysis I concluding that when I decrease the percentage of metal over surface of material, acidity increase (more specifically, strong acidity)...
So, I thought that with increasing of percentage of metal will increase the percentage of acidity, but, this was not like I thought..
I just looking for explanation of this fact, but..... I can't found a very well explanation...
Some one could help me?
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In my experience with zeolites which reveal different Si/Al ratios, the zeolites which contain more Al can store more ammonia since there are more OH-groups available on the surface. Though NH3 is coordinated not so strong on these hydroxyl groups in comparison to the zeolites with higher Si/Al ratios.
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Hi folks.
I have a question regarding Ansys-FLUENT.
I want to simulate heterogeneous reactions taking place in particles of a powder.
The laws governing the kinetic rates are very complex and cannot be reduced to the Arrhenius law or a diffusion law.
Is it possible to create user-defined functions for the reaction rates involving the concentrations/molar fractions of the different solid and gaseous species participating in them?
I see no such option in the heterogeneous reaction interface (see attached picture).
If I must create my own-subroutines and override those of FLUENT, how should I proceed?
Would it be better for me to use another CFD software such as Openfoam?
I'd be truly thankful for your answer.
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If there is a monomial (irreversible reaction) there is no problem to program such an expression in general. If there is a difference between two monomials (reversible reaction), there is also no problem. However, you need either two reaction rate constants or one reaction rate constant and a equilibrium constant (which can be a number, but it can also be a function of temperature and pressure). But it can be the ratio of polynomials (heterogeneous reaction or enzymatic reaction). Then, however, there are too many possibilities to program it in general. So Fortran, for example. You can program any function there. Unfortunately, there is a problem with physicochemical properties. - One can not have everything. Regards,
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Can any one share me some of the reactions involving the carboanions mechanism through heterogeneous catalysts
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You can look for solid base catalyzed Knoevenegal condensation type reaction.
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Kindly explain the major differences between the concept of catalyst inhibitors and catalyst poisons with suitable examples.
Thanks a lot.
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Miroslaw,
I think of fouling as a blockages that cause maldistribution. A burn will sometimes remove a blockage (e.g. if it is coke blocking a pore) but sometimes it will not and dumping and reloading catalyst is often necessary, especially if he blockage is caused by scale/metals instead of hydocarbons.
Coking/carbon disposition is the most common way for commercial Hydrotreating, Catalytic Cracking and Hydrocracking catalyst to lose actiity. Historically these catalyst were :regenerated" with a burn but recently the trend has been to dump catalyst and send it to an offsite regeneration facitity for screnning and coke burning. Arsenic and lead are posons that will permanently deactivate most catalyst and cause them to be unregenerable via burn.
I think of an inhibitor as a material that competes with reactant for catalyst sites inhibition is reversable. If the inhibitor is removed from the feed the rate of the desired reaction will increase. An inhibitor may also increase the rate of coking. If the calayst site is coked up it will usually require a burn(with air or O2) to remove the coke. that has closed up catalysyt pores and/or blocked active sites
.
Poisoning and coking are forms of catalyst deactivation that usually require a stoppage either for regeneration or catalyst replacement.You seem to disagree with the comment it can sometimesbe removed during a regeneration (usually a burn with air or O2). I agree it is not really a "poison" if you can remove it with air/ burn.
All catalyst can be "regenerated" if you take extreme enough measures.
For my purposes - in the refining indusrty- catalyst is not regenerable if activity can not be recovered with a simple burn or other relatively minor procedures like a wash with a solvent.
However even then the active metals can be reclamed and used to make new catalyst.
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Hi everyone, I want to learn how simulate heterogeneous catalytic process, does anyone know any book, review or something where i could start?
Thanks and sorry for the inconvenience
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Hello, Please elaborate you need of simulation a bit more. Both MM and QM and Hybrid QM/MM simulations are possible for any kind of catalysis.
Below is a link and reference to a book for catalytic computation:
Book by RSC
Hope this helps,
Regards
Ajay Khanna
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I want know the best method for calculating Bronsted as well as Lewis acid sites of a catalyst?
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You can make measurements of FTIR using adsorption of pyridine.
Parry, E.P.
An infrared study of pyridine adsorbed on acidic solids. Characterization of surface acidity
(1963) Journal of Catalysis, 2 (5), pp. 371-379
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To clear our concepts, here we have to share our thoughts , experimental results, and refernces to clear the way of action of heterogeneous catalyst... As the science of heterogeneous catalysis is not properly known , lets contribute our sincere efforts.
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Is it more effective for pollutant degradation or transformation?
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Although pollutants degradation is more effective but certain inorganic pollutants cannot be degraded completely. In that case tranformation to less toxic substance would be required.
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Hello all,
I am using pure organic compound with good thermal stability and it is practically insoluble in most of the solvents as catalyst for C-C bond formation. I want to determine its nature in catalysis.
1. I am performing reaction in neat cionditions (without solvent) at 100 C temperature, at this I think some of the catalyst is soluble but I can see most of the catalyst solid present in the mixture.
2. som example reactions due occur at room temp where catalyst is completely insoluble
3. without catalyst reaction won't go, increasing catalyst amount has positive effect. but overloading of catalyst reduced yield.
4. catalyst has amine and carbonyl groups at portals
5. Hot filtration method shows reaction stopped after removing catalyst by filtration.
Now kindly answer following queries,
1. How can I decide my catalyst is heterogeneous or homogeneous?
2. is there any specific test to conduct?
3. Is there any small organic compounds known to act as heterogeneous catalysts?
thank you for your interest and support
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1. Based on your data, the catalyst seems to be heterogeneous. Increasing the catalyst amount does not increase the concentration of the catalyst in solution. "Hot filtration method shows reaction stopped after removing catalyst by filtration" indicates that the true catalyst is not in solution.
2. You have already conducted the "specific test"
3. I don't know, but why not.
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.
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Before irradiation, it is essential for the target pollutants to get adsorbed on the selected photocatalyst by stirring in dark for 30 to 60 minutes. More adsorption on the catalyst reaction site leads to enhanced degradation.
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I would like to carry out research on Enzyme supported magnetically recoverable nanocatalyst systems for Biodiesel production. Homogeneous, heterogeneous and free enzyme based catalyst have main problem of catalyst separation and regeneration. Heterogeneous catalyst solves this issues but active sites of surface molecules can produce leaching in harsh reaction conditions and also it requires centrifuge and filtration techniques. This may give a chance to increase the cost of the products . This is the main challenge for any chemical reaction system. So I am considering Magnetically recoverable nano catalyst or enzyme hybrid catalyst for biodiesel production. This kind of catalyst system can be overcome the challenges of catalyst separation and regeneration of the homogeneous, heterogeneous and enzyme based catalyst system. I provided the challenging issues of biodiesel production to my Prof. But Prof. is not satisfied, my Prof. needs more challenges issues/Breakthroughs in the field. I tried my best level up to my knowledge. I cannot fulfill the requirements of my Prof.
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In my knowledge, there are 4 methods used to produce heterogeneous catalyst for production of biodiesel, which are:
a) Precipitation method
b) Incipient Wet Impregnation method (IWI)
c) Sol-gel method
d) Physical/Direct mixing method
What are the best method and advantage/disadvantage of those methods?
Thank you
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The precipitation method is generally good for producing bulk catalysts with high purity and homogeneity. You will need to separate the catalyst from solution and deal with (depending on scale) large amounts of salt solutions. You have many ways to control the final product (temperature, pH, additives, solvent etc.). Clearly co-precipitation allows you to make, e.g. mixed oxides.
IWI is like WI but involves knowing accurately the volume of solution needed. This will lead to better dispersion of the metal in most cases. There will be no separation, only drying to remove solvent.
Sol-gel will often lead to porous materials with high surface areas. It provides a high degree of control over properties and allows dispersion at the atomic level.
Physical mixing is the simplest method, but as if often the case with the simpler methods, advantages (other than simplicity) are often lacking.
It would be advisable in your case to check some fundamental texts (e.g. Ertl or Krijn de Jong textbooks on catalysis) to understand differences in more detail. Secondly it would be good to think about the properties you need your catalyst to have - stability, high dispersion, simplicity of synthesis for large scale etc.
I hope this answer is useful and if you have any further questions please ask.
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Since, I am pretty sure that no other gaseous product could be formed in the conditions of my experiment except hydrogen, so I am pretty sure that I am able to produce hydrogen (by water reduction). Further, I want to measure the quantity of hydrogen produced during my experiment. Could anyone provide a suggestion of how can I trap hydrogen such that I would be able to measure its quantity as well.
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The method that you use is somewhat dependent on the scale of the experiment in question. For slightly larger scale reactions a gas burette system can be used to very accurately measure evolved hydrogen and many universities have them even in undergraduate teaching labs so they are usually very easy to scrounge up. Before trying to fashion a system yourself ask around to see if any other lab or teaching lab has a working system as this can save you a lot of time and effort to build and celebrate your own system. That being said, if no one in your department has a system then the paper mentioned in the previous comment seams like a really good resource. Here is a paper describing a nice setup but a simple setup can be borrowed or fashioned as well. http://aip.scitation.org.proxy.bc.edu/doi/abs/10.1063/1.2968715?journalCode=rsi
For very small samples GC-MS can be a good option but these instruments are expensive and not every department has one.
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I want to use this powder to impregnate it in multi walled carbon nanotubes.
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Electrochemical preparation of PbO2 is well-known , you can use it to get a thick plate that can be crushed into the desired particle size
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My system is consists of two liquid phase chemicals , it has less yield. When homogeneous graphene suspension is added into this system , yield increases 10 fold. If i want to model this system , should in consider it as heterogeneous or homogeneous ?
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A heterogeneous system can only be described as homogeneous to a pre-specified or required standard error. There will be a minimum mass required to meet that standard error. The standard error can also be determined practically by experiment.
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Please I need suggestions for a good (stable) solid material {other than zeolite or resin} that has acidic functionality or that can be easily modified to behave as such. I want to utilize it as catalyst for esterification reaction in heterogeneous manner at temperatures below 100 deg. C
Thanks in anticipation of your Please I need suggestions for a good (stable) solid material {other than zeolite or resin} that has acidic functionality or that can be easily modified to behave as such. I want to utilize it as catalyst for esterification reaction in heterogeneous manner at temperatures below 100 deg. C
Thanks in anticipation of your contributions. contributions.
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Hello Onyeka,
The attached review article contains the answer of your question.
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I am looking for a convenient method for the hydrogenation of the double bond and reduction of the ketone to an alcohole in (alpha,beta)-unsaturated ketones in one step. The rest are saturated alkane chains. Most likely a cheap mixed catalysator?
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Assuming that there are no other functionality that will interfere with the reaction, the difficultly is usually in achieving complete reduction for both.
Colloidal Palladium Nanoparticles with In Situ H2: Reducing System for α,β-Unsaturated Carbonyl Compounds
Synth. Comm. 2009, 39, 2509
This paper seems to be able to do the reaction as a single step, but is still dependent on other factors.
I think the best bet will be using NaBH4 and varying the solvent and/or additive to achieve your desired conversion.
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Does anyone have experience in heterogenous catalysis of the aldol self-condensation of ketones using niobic acid?
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One can try condensation using Niobic acid (HNbO3), derived from Nb2O5 I hop[e it will behave like P5O5 and enol form of ketone will under go condensation.
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For a heterogeneous catalysis, which reactions may be used as a standard one to examine super acidic catalysts?
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Have you ever heard about Nobel laureate George Olah? Google will help you.
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Hi Scientists!!
I am trying to choose the best model in a experimental arrangement of four factors and three levels.
I don't know what model is more correct? I chose Box-Behken but I am thinking about central-composite design.
I wanna be sure of my election!
Can you help me?
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Hi
Fist of all, why do you want to do a RSM (response surface design) ? being a central composite design, composite design in general, Box-Behken design?
- with this question I mean what do you want to achieve as a result from your experimental work:
A process/synthesis/unit operation optimization should be conducted by some steps
(1) Identify a procedure / method that operate
(2) Conduct a parameterization of the procedure, that is to identify the experimental variables that are possible to variety and the responses that can be measured (yield, selectivity, ….)
(3) Conduct an introductory screening design. In this you commonly identify the solvent, catalyst etc. that you should use. In your case you should consult. the paper by Rolf Carlson and collaborators: Strategies for solvent selection. Acta Chem Scand 1985 B39, 79-91 (and the book by Carlson see below).
When you have performed a screening design, where you should include as many variables as possible. Type of design for this purpose: I suggest you to use a fractional factorial design. By such a design you can identify which variables that are the more important and identify a preliminary optimum.
(4) The preliminary identified optimum might subsequently operate as the centre of a new design that allow you to create a predictive model that allow you to estimate: (a) coefficients for single variables, (b) coefficients for the square of each of the single variables and (c) the coefficients for two-factor interactions of the single variables. I strongly recommend to you to use a response surface design of the type central composite design. This allow you to estimate a model:
y(x1, x2, …, xk) = b0 + b1x1 + b2x2 + … + bkxk + b12x1x2 + b13x1x3 + … + b11x12 + b22x22 + … bkkxk2
Be aware that sometimes, the star points of the central composite design cannot be created; e.g. reaction time -1 (10 min)  0 (25 min) +1 (40 min) will result in that “-2” become a negative time:  -5 min.  In such cases you can solve this by change either the value of (-1) increase the reaction time, shorten the step, i.e. the (0) will be at a smaller value. You can also change the value of the star point.
Introduction of the categorical variables such as: “type of solvents”, “type of catalyst”, “type of reactor”, “type of base”,  etc. should not, from my point of view” be included in a response surface design. In fact, such variables shall be investigated by means of a screening design, where all such parameters (variables) is investigated/compared and decided before you do the response surface deign (a composite design).
Some “bibles” for statistical experimental design, screening and response surface modelling and more:
Design:
Box, G. E. P.; Hunter, J.; Hunter, W. G. Statistics for Experimenters: Design, Innovation, and Discovery, 2nd ed.; 390 Wiley: New York, 2005.
Box, G. E. P.; Draper, N. R. Empirical Model-Building and Response Surfaces; Wiley: New York, 1987.
Model building – regression:
Montgomery, D. C.; Peck, E. A. Introduction to Linear Regression Analysis; Wiley: New York, 1982.
Draper, N. R.; Smith, H. Applied Regression Analysis, 3rd ed.; Wiley: New York, 1998.
Optimization in synthesis:
Design and Optimization in Organic Synthesis, Second Revised and Enlarged Edition
Rolf Carlson Johan Carlson
ISBN: 9780444515278, Elsevier Science, 8th April 2005
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Imagine that there are multiple parallel and series first-order reactions. Which reaction is used to represent the reaction rate in the Thiele modulus equation for a sphere, sqrt(k*a^2/D) on pg 46 of the link? The slowest reaction?
E.g.
1) A->B
2) B->C
3) A->D
4) D->C
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Introducing the Thiele moduli primarily simplifies the form of mass and energy balance equations.
There are no general rules for simplifications of balance equations. One need to consider the rate of reaction / reactions, their reversibility or not and the transport resistances. It is best to use the reaction overall rate / rates when passing from the catalyst grain to the reactor level.
Regards,
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Acid site and metal site can affect together in the reaction condition. So, it can reduce the catalytic activity since the metal nanoparticle sites cannot survive in the presence of acidic situation. 
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I recommend to you, after the preparation of the catalyst to submit it to stability tests. In order to transform the unstable species or tear the active species, and after the stability tests you can prove the catalytic properties in the interest reactions.
In addition, you can determinate the catalytic species who survive to the stability tests.
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My experiments carried out with parameters:
Catalyst supported activated carbon (how to increase CO2 absorption, because I know the preferential adsorption of H2O on catalyst surfaces)
Aqueous phase: I am considering between water, NaHCO3, NaOH (maybe I will try) actually To increase the solubility of CO2 in the aqueous phase, an alkaline medium can be used for photocatalytic reduction of CO2, but I do not How these solutions affect activated carbon when I use it?.
In many papers, deionized water was poured into the reactor and before reactions, the conversion reactor was wrapped with heating tape to provide 80 °C to generate gaseous water. actually, I do not know their goal with this step. 
I appreciate your helping me!
Best regards.
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You posted the second very naive question in this very complex area. Based on your background and your questions you need an experienced  supervisor to guide you in your research. Good luck!
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Metallic Cu is a good catalyst for catalytic conversion of carbonaceous compounds, where C-C bond should be retained and C-O bond cleaves.
A few such reactions are hydrogenolysis of glycerol to 1,2-Propanediol, Photoelectrochemical CO2 reduction etc.
However, it is very difficult to obtain larger BET surface area of Cu nanoparticles unlike noble metals such as Pt, Ru.
What are the best possible ways to obtain larger surface? Nanostructuring, templating or using support are a few possible ways, what I know. I draw your attention on this for best fit. 
What is the limiting factor in obtaining the larger surface area of Cu?
Is there a way to retain them in the metallic state without oxidizing for a longer time? 
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Thanks Prof. Yuri Mirgorod for your answer.
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The sonication and centrifugation process of TMDs in different solvents, has been widely reported. Coleman suggests that NVP is the best solvent to use, however I can´t find info on how to evaporate/remove the NVP. 
Thanks.
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Hi,
It depend on MW of your polymer. NVP with low polymer weight can be easily decomposed in a controlled atmosphere furnace under neutral atmosphere of N2 or Ar without any alteration in MoS2.
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Hi!
I'd like to selectively trap H20, VOC and CO2 and not H2 for a H2 detection application.
There is no possibilities to use zeolites or organic polymers in cause of radiations and heterogeneous catalytic reactions.
Does anybody can give me some lines to fix ma problem ? Do Activated charcoals can be used for this (wirth high amount of micropores)?
thanks a lot!
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Try liquid nitrogen trap
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The reaction is CO methanation(i.e CO + 3H2 = CH4 + H2O). Since the input gases are CO2 and H2 at the surface of catalyst, the rate of former reaction is zero. As CO2 methanation and Reverse water-gas shift occurs along the radius of catalyst towards the center CO, H2O and CH4 are formed which will initiate the CO methanation reaction which was initially zero at the surface of the catalyst.
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Dear Pratheek,
Example –1Turnover Frequency in Fischer–Tropsch Synthesis
CO   +  3H = 2 CH 4 +     H 2 O
The Fischer–Tropsch synthesis was studied using a commercial 0.5 wt % Ru on  -Al 2 O 3 . The catalyst dispersion percentage of atoms exposed, determined fromhydrogen chemisorption, was found to be 49%.At a pressure of 988 kPa and a tem-perature of 475 K, a turnover frequency, , of 0.044 s  l  was reported for methane.What is the rate of formation of methane, , in mol/s  g of catalyst (metal plus sup-port)?
See this file
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In hydrogenation process of phenylacetylene over Pd/C catalyst, when we calculate TON and TOF, we need to calculate the active site in the Pd/C catalyst.
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Hi Hussein Al-Wadhaf,
You can determine the number of active site of deposited metals by H2-pulse chemisorption measurements, and their strength by further H2-TPD analysis; both analysis can be performed in sequence. Although H2 is the most applied probe, it can be replaced by other probe molecules such as CO and NO. The choice of which probe to use depends on the adsorption mechanism, I know that the use of H2 to determine active sites on nobel metals like Ru and Os works well. However I believe that CO is a better probe molecule for Pd. I did a quick check and it seems that H2 embrittle Pd. I have included here links that might help in your studies.
Best Regards,
Alexandre.
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Concerning the surface of the zeolit, it should be composed by silanol groups and some bronsted sites - as Si-OH-Al... But I would like to know if we can find groups as Al-OH on the surface...Any reference proving that?
How to characterize?
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The Presence of OH group can be determined by FTIR spectroscopy. The OH group stretching band appears between 3200 t0 3600 cm-1. The wavelength position depends on whether the hydroxyl group is free or hydrogen bonded to nearby OH groups. Make KBr pellets and scan sample from 400 cm-1 to 4000 cm-1. If you want to quantify the OH groups, you should have a standard sample that contains OH groups in the same environment as in the sample.
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Extrudates of Al2O3 were impregnated with solution H2PtCl6 to obtain yellowish material with 0.3 mass % Pt. Impregnated extrudates were dried (60 0C) during 5 h resulting in dried extrudates of the same yellowish colour. Dried extrudates were calcined (450 0C) at air athmosphere during 5 h resulting in calcined extrudates of different colours: some of them still yellowish, some of them are grey, some black etc.
Why?
Thanks
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I suppose it is due to agglomeration of small crystallites into bigger ones. 
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what the rate-determining step for the PROX over Au catalysts. CO chemisorption? oxygen dissociation?
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Thank you so much
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I have prepared Ir-Sn bimetallic nanoparticles and have used them as catalyst in some oxidation reactions. now i want to find the turnover frequency of the catalyst. but i do not know the parameters of my particles. can anyone suggest me some other way to find the TOF of the catalyst? 
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thank you for the help everyonee
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Assume the gas is some inert gas and the substrate is V2O5 nanostructure.
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I believe you meant to say Gas Adsorption Analysis instead of BET method. BET method does not tell you if the molecule is chemisorbed or physisorbed. The BET method is an equation, nothing else, which a Gas Adsorption data is used to obtain the specific surface area. The BET method considers the multi-layer adsorption of an inert gas onto a flat and energetically homogeneous surface.  These assumption are rare, and therefore the C constant of the BET equation must be carefully discussed. Additionally, the relative pressure range used to calculate surface area must provide a linear fit. IUPAC recommends P/Po between 0.05 to 0.35. I particularly use 0.05 to 0.2 when there is no micropores (with at least 6 data points). 
Regards to the analysis in question there is no universal method, you need to think about what kind of adsorption sites you want to analyse. If an inert gas is used, there will be no chemisorption, mainly at temperatures above the condensation temperature. If you desire to obtain information about the adsorption strength of a chemisorbed molecule, the Temperature-Programmed Desorption (TPD) is a good start. For instance, you can use NH3-TPD to evaluate acid sites and CO2-TPD to evaluate basic sites. Also, your sample must be stable at the temperature you are using for analysis. More discussions about this method can be found in this paper (DOI: 10.1021/acsami.6b15507), and references therein [Ref 55-58]. Some times a second source of characterization is needed, such as TPD coupled with a FTIR detector. Moreover, this review (DOI: 10.1021/cm0101069) has being sited more thand 1500 times and discuss the adsorption on nanostructured materials. You may find it useful.
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Working on designing the Cativa process but can not figure out the kinetics, really would appreciate the help. 
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Dear Elizabeth,
Have you found the pre exponential factor?
If yes could you please share it with me?
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For gas phase reactions, such as cracking or methanol-to-olefins, the introduction of  mesopores (2 - 50 nm) and/or macropore (>50 nm) into zeolite structure leads to the occurence of Knudsen diffusion mechanism since diffusion relies on wall collisions to direct molecular flow.
Does this diffusion also occur when hierarchical zeolite used as catalyst in liquid phase reaction, i.e. self condensation of cylohexanone??
Please refer me to articles or books regarding the diffusion of organic liquid phase reaction in hierarchical zeolites.
Thank you
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view the article of sheldon in the hetrogeneous catalysis 
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