[Show abstract][Hide abstract]ABSTRACT: Graphitic carbon nitride nanosheets were investigated for developing effective Pt catalyst supports for selective hydrogenation of furfural to furfuryl alcohol in water. The nanosheets with an average thickness of about 3 nm were synthesized by a simple and green method through thermal oxidation etching of bulk g-C3N4 in air. Combined with the unique feature of nitrogen richness and locally conjugated structure, the g-C3N4 nanosheets with a high surface area of 142 m2 g−1 were demonstrated to be an excellent supports for loading small-size Pt nanoparticles. Superior furfural hydrogenation activity in water with complete conversion of furfural and high selectivity of furfuryl alcohol (>99%) was observed for g-C3N4 nanosheets supported Pt catalysts. The large specific surface area, uniform dispersion of Pt nanoparticles and the stronger furfural adsorption ability of nanosheets contributed to the considerable catalytic performance. The reusability tests showed that the novel Pt catalyst could maintain high activity and stability in the furfural hydrogenation reaction.
[Show abstract][Hide abstract]ABSTRACT: The direct reductive amination of carbonyl compounds with NH3 and H2 is an alternative route to produce primary amines in practical production. The search for efficient and selective catalysts has attracted great interest. In the present work, the reductive amination of heptaldehyde with NH3 was investigated over a Ru-based catalyst. The product selectivities were found to be related with the supports of Ru. The alumina with spinel structure (γ-Al2O3, θ-Al2O3)-supported Ru catalysts exhibited selectivity favoring primary amines (94% yield) at 100% heptaldehyde conversion under optimal conditions. Purely basic (MgO, CaO) and relative acidic (Nb2O5, SnO2, MCM-41, HZSM-5) supports showed relatively poor selectivity towards primary amines (0%–53% yield). The reductive amination mechanism was also proposed. The Schiff base N-[heptylene]heptyl-1-amine was a key intermediate. Ru/γ-Al2O3 was shown to be an excellent hydrogenolysis catalyst to selectively produce primary amine by amination and hydrogenolysis of N-[heptylene]heptyl-1-amine.
[Show abstract][Hide abstract]ABSTRACT: Ruthenium (Ru) supported on activated carbon (AC) and carbon nanotubes (CNTs) was carried out in the hydrogenolysis of sorbitol to ethylene glycol (EG) and 1,2-propanediol (1,2-PD) under the promotion of tungsten (WOx) species and different bases. Their catalytic activities and glycols selectivities strongly depended on the support properties and location of Ru on CNTs, owning to the altered metal-support interactions and electronic state of ruthenium. Ru located outside of the tubes showed excellent catalytic performance than those encapsulated inside the nanotubes. Additionally, the introduction of WOx into Ru/CNTs significantly improved the hydrogenolysis activities, and a complete conversion of sorbitol with up to 60.2% 1,2-PD and EG yields was obtained on RuWOx/CNTs catalyst upon addition of Ca(OH)2. Stability study showed that this catalyst was highly stable against leaching and poisoning and could be recycled several times.
[Show abstract][Hide abstract]ABSTRACT: In this work, modification of graphitic carbon nitride photocatalyst with acid was accomplished with a facile method through reflux in different acidic substances. The g-C3N4-based material was found to be a metal-free photocatalyst useful for the selective oxidation of benzyl alcohol with dioxygen as the oxidant under visible light irradiation. Acid modification had a significant influence on the photocatalytic performance of g-C3N4. Among all acid tested, sulfuric acid-modified g-C3N4 showed the highest catalytic activity and gave benzaldehyde in 23% yield for 4 h under visible light irradiation, which was about 2.5 times higher than that of g-C3N4. The acid modification effectively improved surface area, reduced structural size, enlarged band gap, enhanced surface chemical state, and facilitated photoinduced charge separation, contributing to the enhanced photocatalytic activity. It is hoped that our work can open promising prospects for the utilization of metal free g-C3N4-based semiconductor as visible-light photocatalyst for selective organic transformation.
[Show abstract][Hide abstract]ABSTRACT: Ru particles were introduced into the zeolite ZSM-5 (MFI) by either a conventional impregnation method or a one-step template-free process. The resultant materials were characterized by X-ray diffraction, N2 adsorption-desorption, scanning electron microscopy, transmission electron microscopy, NH3 and CO2 temperature-programmed desorption. The results indicated that the Ru species in ZSM-5 catalysts prepared via the latter approach (designated as Ru/ZSM-5-TF) were highly dispersed in the ZSM-5 framework structure and this material exhibited high catalytic performance during the hydrogenation of D-glucose to D-sorbitol. The conversion of D-glucose was as high as 99.6% with D-sorbitol selectivity reaching 99.2%, exceeding the performance of Ru/ZSM-5 catalysts prepared by the conventional impregnation method with microporous or desilicated ZSM-5 supports. More importantly, this catalyst showed high stability against leaching and poisoning and could be reused several times. The extensive dispersion of the Ru species, strong interaction between the Ru species and the ZSM-5, and the suitable surface acidity-basicity balance of the Ru/ZSM-5-TF were all critical factors leading to excellent catalytic behavior and stability.
[Show abstract][Hide abstract]ABSTRACT: Mesoporous SBA-15 materials functionalized with propylsulfonic acid groups (SBA-15-SO(3)H) were synthesized through a conventional one-pot route. It was used as a catalyst for the selective synthesis of 5-hydroxymethylfurfural (HMF) from the dehydration of fructose using BmimCl as solvent. Reaction time, temperature and fructose concentration were investigated during the HMF synthesis procedure. The catalyst SBA-15-SO(3)H exhibits high fructose conversion (near 100%) and HMF selectivity (about 81%) with good stability in the HMF synthesis. It was a suitable catalyst to produce HMF from renewable carbohydrates in potential industrial process.
[Show abstract][Hide abstract]ABSTRACT: Low melting systems consisting of ammonium salts and highly concentrated fructose were used for the conversion of fructose into 5-hydroxymethylfurfural (HMF). Not only acting as solvents, at sufficiently high temperatures, the ammonium salts themselves could also catalyse the dehydration of fructose to HMF. Among those salts, tetraethyl ammonium chloride (TEAC) was found to be the most efficient solvent-catalyst, demonstrated by its ability to achieve 81.3% HMF yield with 33.3wt% fructose concentration at 120°C. 79.2% HMF yield was obtained with 50wt% fructose concentration in the TEAC/fructose system using 5mol% NaHSO4·H2O as a co-catalyst. A semi continuous biphasic system of TEAC/fructose/NaHSO4·H2O melt using tetrahydrofuran (THF) to recover HMF was proposed and demonstrated in a laboratory scale process operating at 120°C. The impurities in the HMF recovered, involving TEAC and NaHSO4·H2O, were determined using 1H NMR, elemental analysis and ICP-OES.
[Show abstract][Hide abstract]ABSTRACT: Conversion of fructose and glucose into 5-hydroxymethylfurfural (HMF) was investigated in various imidazolium ionic liquids, including 1-butyl-3-methylimidazolium chloride (BmimCl), 1-hexyl-3-methylimidazolium chloride (HmimCl), 1-octyl-3-methylimidazolium chloride (OmimCl), 1-benzyl-3-methylimidazolium chloride (BemimCl), 1-Butyl-2,3-dimethylimidazolium chloride (BdmimCl), and 1-butyl-3-methylimidazolium p-toluenesulfonate (BmimPS). The acidic C-2 hydrogen of imidazolium cations was shown to play a major role in the dehydration of fructose in the absence of a catalyst, such as sulfuric acid or CrCl(3). Both the alkyl groups of imidazolium cations and the type of anions affected the reactivity of the carbohydrates. Although, except BmimCl and BemimCl, other four ionic liquids could only achieve not more than 25% HMF yields without an additional catalyst, 60-80% HMF yields were achieved in HmimCl, BdmimCl, and BmimPS in the presence of sulfuric acid or CrCl(3) in sufficient quantities.
[Show abstract][Hide abstract]ABSTRACT: The complete catalytic cycle of the reaction of glucose conversion to 5-hydroxymethylfurfural (HMF) by metal chlorides (MCl3) in 1-butyl-3-methylimidazolium chloride ([BMIM]Cl) ionic liquid has been studied using density functional theory (DFT) calculations. Insights into the most preferred mechanistic pathways were gained for both isomerization of glucopyranose to fructofuranose as well as subsequent dehydrations of fructofuranose to the final product HMF, which were considered as two main reactions in the whole process. The first part of the mechanism was predicted to proceed slowly and thermodynamically less favored. A five-membered-ring chelate complex of the metal atom with glucopyranose was assumed as a key intermediate. The second part consists of sequential releases of three water molecules from fructofuranose. The removal of the first water appears to be rate controlling, whereas further loss of the second and third water were highly exothermic. A variety of transition metal cations in the same oxidation states (WCl3, MoCl3, and FeCl3) were screened and parallel DFT studies were carried out to determine their reactivities in the catalytic reaction. It turns out that the metal centers exerted significant influences on the stabilities of the intermediates as well as the energy barriers associated with each elementary reaction step. The overall free energy barriers at 353K indicated that the reaction activities of the entire processes over different MCl3 active sites decrease in the order of WCl3>MoCl3>CrCl3>FeCl3, in which WCl3 may be the most promising catalyst at low temperatures.
Article · Feb 2011 · Computational and Theoretical Chemistry
[Show abstract][Hide abstract]ABSTRACT: Mesoporous SBA-15 functionalized with zinc carboxylate (ZC/SBA-15) was used as a heterogeneous catalyst for the selective
synthesis of methyl-4,4′-di(phenylcarbamate) (MDC) from dimethyl carbonate (DMC) and 4,4′-methylenedianiline (MDA). ZC/SBA-15
was prepared in three steps: first, SBA-15 grafted with –CN group was synthesized via the conventional one-pot route; then
the –CN group was converted into –COOH group in H2SO4 solution; lastly, Zn2+ ions were introduced into the material by a facile ion-exchange process. The catalyst ZC/SBA-15 exhibits high MDA conversion
(near 100%) and MDC selectivity (about 86.5%) with good recyclability in the MDC synthesis; this may provide a new approach
for the non-phosgene synthesis of isocyanates.