Homogeneous Catalysis

Homogeneous Catalysis

  • James Woods added an answer:
    What are the best methods for quantifying headspace CO and H2?

    I am curious if anyone has had any luck quantifying headspace CO and/or H2 using any methods besides GC. Are there any methods out there that are accurate, efficient, and relatively inexpensive? I am planning on using GC but was curious if there was some other method I was missing. 

    James Woods · Carnegie Mellon University

    I've used a gas-phase mass spectrometer to analyze carbon monoxide, carbon dioxide, and hydrogen content. It was at least as accurate as a GC and had the benefit of being significantly faster. Stanford research makes all-in-one units like a QMS-200 that can interface using their software or LabView.

  • Aaron Bloomfield added an answer:
    Can anyone suggest a simple protocol of esterification/transesterification of a glyceride using n-butanol as the solvent, as well as the catalyst?
    For a high yield of an ester, a catalyst that will give an optimum yield is needed in the esterification reaction.
    Aaron Bloomfield · Yale University

    Acids like H2SO4 or acidic resins like sulfonated polymers (Dowex, Nafion etc.) can catalyze trans-esterification. So can alkaline salts like NaOH, Ca(OH)2 and KOH... It depends what the substrates are, and what sort of other limitations there are on the reaction...

  • Can anyone provide a good homogenization method for UHMWPE into HDPE matrix at molecular level?

    Can anybody help to mix 0 - 5 wt %  UHMWPE (having molecular weight 2 to 15 Million) with HDPE (molecular weight of 3 to 5 lakhs) at molecular. We tried different methods by melt blending, changing screw configuration etc but we are seeing the UHMWPE particles in HDPE matrix.

    Gandham satya srinivasa Rao · Reliance Industries Limited

    Thanks for your nice suggestion.... but  the solubilityof polyolefins is very low  may not be viable  economically and environmental friendly..

  • Simone Ripandelli added an answer:
    Does anybody work with organometallic Palladium Neocuproine as a homogeneous catalyst?

    I am looking for someone which works with Palladium organometallic complex to share our experience with.

    Simone Ripandelli · Politecnico di Torino

    Sorry again. I observed the mirror palladium only when the catalyst reacts with diols.

    I do not use the dry ACN...maybe it is the problem!

    I know that waiting a lot of side products appear, but I wait in order to abtain the activate ACN.

    I'am going to do some evaluation and experiments, thanks a lot for your time.

    Simone

  • Nidal Saleh added an answer:
    What NMR solvent is the best for working at temperatures of 333-393K?
    I need to do some kinetic work on a ruthenium complex, and in need of a suitable solvent that will not interact with the complex or any of the substrates.
    Nidal Saleh · Université de Rennes 1

    I have already done some with Ru complexes and deuterated toluene was perfect

  • Chiranjeev Sharma added an answer:
    What is the difference between a homogenous and heterogeneous catalysis?
    If the catalyst used is solid which dissolves in the reaction mixture and cannot be separated or recycled/reused will it still be called heterogeneous catalyst.
    Further, if it is heterogeneous catalyst is it a rule that you should be able to reuse the catalyst. While reporting a new catalytic system or a new application of existing catalyst, how to convince reviewers for the acceptance if we are unable to reuse the catalyst?
    Chiranjeev Sharma · University of Delhi
    Dear All. Thank you for your responses.
    To be precise I am trying to synthesize some peroxides using MTO as a mild catalyst in trifluoroethanol. 30% H2O2 is also used along with the addition of Ethereal HBF4. The reaction does proceed well and I do am able to get some product. However, from catalytic point of view I'm uncertain about how to recover the catalyst or reuse it from the reaction mixture.
    Now, is it just to say that I'm doing a homogeneous catalysis or the reaction should be considered heterogeneous??
  • Imre Tóth added an answer:
    How do I calculate TON and TOF?
    For a homogeneous catalyst, I have two formulas to calculate the TON:
    Moles of substrate converted/moles of catalyst or moles of product/moles of catalyst.
    Which one shall I use knowing that the there are also many side reactions?

    For the TOF, can I use the time of full conversion?
    Imre Tóth · University of Pannonia, Veszprém
    You are welcome Nesrine. The slope of the substrate conversion curve depends also on the reaction rate (thus also not an exact measure). For this reason it doesn't really matter whether you take the slope or a single point at low conversion (this is easier). As earlier said, the best is to give the reaction profile (conversion, selectivity vs reaction time as well, so that everybody can calculate whatever she/he wants to.
  • Hamidreza Samouei added an answer:
    How could it be possible to observe zero-order on the metal center in a homogeneous system?
    In stoichiometric homogeneous reaction with metal complexes for activation of inert bonds how could it be possible to observe zero order dependence on the metal center?
    Hamidreza Samouei · Texas A&M University
    Regarding catalysis by metal particles, based on mercury test no change was observed.
  • Reza Fazaeli added an answer:
    Photocatalytic activity over smooth and rough surfaces: Which one should be better?
    I got good results over smooth surfaces for photocatalytic reduction of CO2. What is the general perception about such reactions on different surfaces i.e. smooth and/or rough?
    Reza Fazaeli · Islamic Azad University
    The photocatalytic activity of a photocatalyst depends on several factors. So Just smoothness or roughness of the surface is not a comprehensive criterion for judgment about photocatalytic performance.
    Is your photocatalyst is an intrinsic semiconductor or a doped semiconductor? How much is the available surface for exposure of UV/Vis. light? What about the sensitizers of your designed photocatalyst?
    Although, it is obvious the the surface area of a rough surface is more than the smooth one, but in the case of photocatalysts, the effective surface (i.e. surface could absorbed the light) is more important regarding to your purpose.
  • Sepurahman . added an answer:
    How can I explain acidity of a catalyst with FTIR without pyridine adsorption?
    Is it possible to explain it with an OH band?
  • Ahmed F. Abdel-Magied added an answer:
    How can you prove that clusters are the real catalyst on homogeneous catalysis?
    After finishing the catalysis process and recovering your catalyst, you will never get exactly the same mass balance. So, how can you prove that your cluster is the active catalyst, not a decomposed mononuclear species?
    Ahmed F. Abdel-Magied · Lund University
    Thanks a lot. Sounds really interesting. I will take a look to this book.
  • "Cocktail of catalysts" in cross-coupling and other organic reactions?
    It seems that many cross-coupling and Heck reactions operate as "cocktail of catalysts" system (multiple species catalysis in solution). http://pubs.acs.org/doi/abs/10.1021/jo402038p
    Are there other catalytic reactions that involve multiple species in the catalytic cycles? Was it observed experimentally?
    Francisco Jose Tôrres Aquino · Universidade Federal de Uberlândia (UFU)
    Peharps you can use the methodology for povarov reaction type using calix[4]arene.
    Fernandes et. al. Organic and biomolecular chemistry, 2013,11, 5069.
  • Valentine P. Ananikov added an answer:
    What is cluster catalysis?
    The question concerns organic reactions catalyzed by transition metal clusters. What is a definition of cluster in this regard? I see many controversial descriptions in the literature. It should be somewhere between mononuclear metal complex and nanoparticle. Metal cluster should contain a minimum of three (or two?) metal atoms. However, what is the upper size limit of cluster? (i.e. the border between cluster and nanoparticle). I would very much appreciate the references, where a clear definition of metal cluster is given. Thanks!
    Valentine P. Ananikov · Russian Academy of Sciences
    Thanks! The reference on Phil. Trans. R. Soc. is very useful (special issue on clusters).
  • Gabriel S. Gusmão added an answer:
    What are the specific and common features for homogeneous and heterogeneous catalysis in its nature, kinetics, effect of external conditions, etc?
    Both these phenomena are termed catalysis, but clear and complete discussion and specification of their similar and distinguishing features would be useful.
    Gabriel S. Gusmão · University of Campinas
    As far as I picture catalysis, there is not such a limiting difference between heterogeneous and homogeneous catalysts. You could think of a homogeneous catalysts as phase-dispersed heterogeneous catalyst. In the same fashion, one could eventually calculate coverage of "phase-dispersed catalysts", being these metal-complexes, metallocenes or even enzymes.
    The role of catalysts does not change though. They are responsible for lowering activation barriers necessary for a reaction to happen, even though, thermodynamically speaking, they will not make a non-spontaneous reaction to spontaneously take place.
    As previously mentioned by Kyle, although both should primarily entail elementary steps and may or may not be hindered by mass transfer limitation, there are some specific parameters which are determinant in catalytic activity.
    With regard to heterogeneous catalysts, surface area is directly related to the turnover frequency/rate, but other slight changes in catalyst geometric features might completely change the reaction mechanism and hence selectivity. For instance, you may have a metal supported catalyst in which the amount of metal impregnated/deposited over it would lead to different metal particle sizes/diameters, changing the energetics between metal/support, potentially driving kinetics to different ends. In the same scenario, your support, assuming a metal oxide such as TiO2 having a band-gap in the UV-region could pump up electrons to the d-band of the transition metal supported by it, boosting a reaction that were already taking place or allowing for a more energy-demanding mechanism to develop. As for where to look, for thermocatalysis, look up phononics, and for photocatalysts, plasmonics.
    I do not have much experience in homogeneous catalysts, but I would say that free-radicals, chain-reactions (polymerization), protonation (acid catalysis), active site reachability (enzymes) are factors/events you should look at.

    If you are interested in heterogenous catalysts I can send you some references which thoroughly expand on it.

    Best regards,
    Gabriel
  • Pavan Kumar Mandali added an answer:
    What differences are there in the reaction mechanisms compared with the Pd ions or complexes and Pd nanoparticles in sonogashira coupling reactions?
    Reaction mechanisms.
    Pavan Kumar Mandali · Indian Institute of Technology Madras
    Thank you very much for your answer.. It is really helpful.
  • Sudheesh N added an answer:
    How can safe injection be performed to Gas Chromatography?
    I mean how can we make clean our sample before injection? As we know, the cleaner our sample in terms of particles or abrasive chemicals, the longer our column can be used. Although i am aware of the necessity of clear sample, i do not have any practice. Bacause İ study small amount so İ can not filter. also filtering may cause different effect of composition.
    Sudheesh N · NSS College
    Centrifuge! you can use micro centrifuge to get clean sample.
  • Domenico Venuti added an answer:
    Which effect the amount of substrate in a catalytic reaction?
    Effect of substrate.
    Domenico Venuti · Central University of Venezuela
    It can indicate that the sustrate coordinates or interacts in any way with the catalyst previous to the determinat velocity step. You will need also check if you are in a thermodinamic or cinetical regime.
  • Nader Ghaffari Khaligh asked a question:
    Can anyone recommend a review for sulfonic acids and sulfamides as catalysts in organic chemistry?
    Application of sulfonic acids and sulfamides as catalyst.

About Homogeneous Catalysis

In chemistry, homogeneous catalysis is a sequence of reactions that involve a catalyst in the same phase as the reactants.

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