TiO2-Supported Re as a General and Chemoselective Heterogeneous Catalyst for Hydrogenation of Carboxylic Acids to Alcohols

TiO2-supported Re, Re/TiO2, was found to promote selective hydrogenation of carboxylic acids having aromatic and aliphatic moieties to the corresponding alcohols. Re/TiO2 showed superior results compared to other transition-metal-loaded TiO2 and supported Re catalysts for selective hydrogenation of 3-phenylpropionic acid. 3phenylpropanol was produced in 97% yield under mild conditions (5 MPa H-2 at 140 degrees C). Contrary to typical heterogeneous catalysts, Re/TiO2 does not lead to the formation of dearomatized byproducts. The catalyst is recyclable and shows a wide substrate scope in the synthesis of alcohols (22 examples; up to 97% isolated yield)

Selective C3-alkenylation of oxindole with aldehydes using heterogeneous CeO2 catalyst

We report herein that a commercially available CeO2 is an active and reusable catalyst for the C3-selective alkenylation of oxindole with aldehydes under solvent-free conditions. This. catalytic method is generally applicable to different aromatic and aliphatic aldehydes, giving 3-alkyledene-oxindoles in high yields (87%-99%) and high stereoselectivities (79%-93% to E-isomers). This is the first example of the catalytic synthesis of 3-alkenyl-oxindoles from oxindole and various aliphatic aldehydes. The Lewis acid-base interaction between Lewis acid sites on CeO2 and benzaldehyde was studied by in situ IR. The structure-activity relationship study using CeO2 catalysts with different sizes suggests that defect-free CeO2 surface is the active site for this reaction. (C) 2020, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved

Catalytic Methylation of Aromatic Hydrocarbons using CO2/H2 over Re/TiO2 and H-MOR Catalysts

A combined catalyst comprising TiO2-supported Re (Re(1)/TiO2; Re=1 wt\%) and H-MOR (SiO2/Al2O3=90) was found to promote the methylation of benzene using CO2 and H2. This catalytic system exhibited high performance with regard to the synthesis of methylated benzenes and gave high yields of total methylated products (up to 52 \% benzene-based yield and 42 \% CO2-based yield) under the reaction conditions employed in this study (pCO2=1 MPa; pH2=5 MPa; T=250 °C; t=20 h) in a batch reactor. Catalyst screening demonstrated that a combination of Re(1)/TiO2 and H-MOR (SiO2/Al2O3=90) exhibited superior performance compared to other combinations of supported metal catalysts and zeolites in terms of both yield and selectivity for methylated benzenes

Reverse Water-Gas Shift Reaction via Redox of Re Nanoclusters Supported on TiO2

A Re catalyst supported on TiO2 (Re/TiO2) promoted the reverse water-gas shift (RWGS) reaction, exhibiting high selectivity toward CO. Operando X-ray absorption near edge structure (XANES) measurements revealed that the redox of Re species was responsible for promotion of the reaction. The Re/TiO2 catalyst also possessed remarkable durability and maintained >99.9% CO selectivity for more than 1000 h

Reverse water-gas shift reaction over Pt/MoOx/TiO2 : reverse Mars-van Krevelen mechanism via redox of supported MoOx

The reverse water-gas shift (RWGS) reaction is a promising catalytic route for reducing CO2 emissions because its product, CO, is a key intermediate in various industrialized catalytic processes that produce fuels and chemicals. We describe herein a MoOx/TiO2-supported Pt catalyst (Pt(3)/MoOx(15)/TiO2; Pt loading = 3 wt%, MoO3 loading = 15 wt%) that promotes the RWGS reaction at low temperature (200-300 degrees C) with high activity and selectivity. The catalytic performance for both CO2 conversion and selectivity of Pt(3)/MoOx(15)/TiO2 is better than those of Pt catalysts on other supports and other metal catalysts supported on MoOx(15)/TiO2, as well as Cu- and Fe-Cr-based industrial catalysts. Moreover, results of operando X-ray absorption spectroscopy studies show that the reaction takes place via the reverse Mars-van Krevelen mechanism where H-2 acts as a reducing agent to create oxygen vacancies on the supported Mo oxide species that are filled by CO2 as an oxidizing agent

Direct Phenolysis Reactions of Unactivated Amides into Phenolic Esters Promoted by a Heterogeneous CeO2 Catalyst

The direct catalytic esterification of amides that leads to the construction of C-O bonds through the cleavage of amide C-N bonds is a highly attractive strategy in organic synthesis. While aliphatic and aromatic alcohols can be readily used for the alcoholysis of activated and unactivated amides, the introduction of phenols is more challenging due to their lower nucleophilicity in the phenolysis of unactivated amides. Herein, we demonstrate that phenols can be used for the phenolysis of unactivated amides into the corresponding phenolic esters using a simple heterogenous catalytic system based on CeO2 under additive-free reaction conditions. The method tolerates a broad variety of functional groups (>50 examples) in the substrates. Results of kinetic studies afforded mechanistic insights into the principles governing this reaction, suggesting that the cooperative effects of the acid-base functions of catalysts would be of paramount importance for the efficient progression of the C-N bond breaking process, and consequently, CeO2 showed the best catalytic performance among the catalysts explored

Mechanistic study of the selective hydrogenation of carboxylic acid derivatives over supported rhenium catalysts

The structure and performance of TiO2-supported Re (Re/TiO2) catalysts for selective hydrogenation of carboxylic acid derivatives have been investigated. Re/TiO2 promotes selective hydrogenation reactions of carboxylic acids and esters that form the corresponding alcohols, and of amides that generate the corresponding amines. These processes are not accompanied by reduction of aromatic moieties. A Re loading amount of 5 wt% and a catalyst pretreatment with H-2 at 500 degrees C were identified as being optimal to obtain the highest catalytic activity for the hydrogenation processes. The results of studies using various characterization methods, including X-ray diffraction (XRD), X-ray absorption fine structure (XAFS), X-ray photoelectron spectroscopy (XPS), and scanning transmission electron microscopy (STEM), indicate that the Re species responsible for the catalytic hydrogenation processes have sub-nanometer to a few nanometer sizes and average oxidation states higher than 0 and below +4. The presence of either a carboxylic acid and/or its corresponding alcohol is critical for preventing the Re/TiO2 catalyst from promoting production of dearomatized byproducts. Although Re/TiO2 is intrinsically capable of hydrogenating aromatic rings, carboxylic acids, alcohols, amides, and amines strongly adsorb on the Re species, which leads to suppression of this process. Moreover, the developed catalytic system was applied to selective hydrogenation of triglycerides that form the corresponding alcohols

Selective Transformations of Triglycerides into Fatty Amines, Amides, and Nitriles by using Heterogeneous Catalysis

The use of triglycerides as an important class of biomass is an effective strategy to realize a more sustainable society. Herein, three heterogeneous catalytic methods are reported for the selective one-pot transformation of triglycerides into value-added chemicals: i) the reductive amination of triglycerides into fatty amines with aqueous NH3 under H-2 promoted by ZrO2-supported Pt clusters; ii) the amidation of triglycerides under gaseous NH3 catalyzed by high-silica H-beta (H beta) zeolite at 180 degrees C; iii) the H beta-promoted synthesis of nitriles from triglycerides and gaseous NH3 at 220 degrees C. These methods are widely applicable to the transformation of various triglycerides (C-4-C-18 skeletons) into the corresponding amines, amides, and nitriles

Catalytic Methylation of Aromatic Hydrocarbons using CO 2

A combined catalyst comprising TiO2-supported Re (Re(1)/TiO2; Re=1 wt\%) and H-MOR (SiO2/Al2O3=90) was found to promote the methylation of benzene using CO2 and H2. This catalytic system exhibited high performance with regard to the synthesis of methylated benzenes and gave high yields of total methylated products (up to 52 \% benzene-based yield and 42 \% CO2-based yield) under the reaction conditions employed in this study (pCO2=1 MPa; pH2=5 MPa; T=250 °C; t=20 h) in a batch reactor. Catalyst screening demonstrated that a combination of Re(1)/TiO2 and H-MOR (SiO2/Al2O3=90) exhibited superior performance compared to other combinations of supported metal catalysts and zeolites in terms of both yield and selectivity for methylated benzenes