Liquid-phase Hydrogenation Of Benzaldehyde Research Articles

Liquid-Phase Hydrogenation of Benzaldehyde on Low-Percentage Pt-Containing Catalysts under Mild Conditions

The reaction of the liquid-phase hydrogenation of benzaldehyde is studied in two modes: at room temperature and atmospheric pressure, and at a temperature of 70°С and a pressure of 0.5 MPa on Pt/CeO2–ZrО2 catalysts with metal contents of 1 to 0.025 wt %. A 96% conversion of benzaldehyde is obtained on 1% Pt/CeO2–ZrО2 catalysts at room temperature, while a 97% conversion is obtained on 0.1% Pt/CeO2–ZrО2 catalysts at elevated temperatures. The selectivity of the formation of benzyl alcohol is in all cases 100%.

The Application of Attenuated Total Reflection Infrared Spectroscopy to Investigate the Liquid Phase Hydrogenation of Benzaldehyde Over an Alumina-Supported Palladium Catalyst

The hydrogenation of benzaldehyde in cyclohexane over a 5 wt% Pd/Al2O3 catalyst at 313 K is firstly investigated at ambient pressure in a stirred batch reactor. The formation of benzyl alcohol is a facile process and a small mass imbalance is indirectly attributed to the formation of benzene as a by-product. No hydrogenolysis reaction to form toluene is observed. Secondly, examination of this reaction system by attenuated total reflection infrared (ATR-IR) spectroscopy enables the chemistry at the liquid/solid interface to be probed. Specifically, the ν(C=O) modes of solvated and adsorbed benzaldehyde are evident at 1712 and 1691 cm−1 respectively, providing information on how the reagent is partitioning within the reaction medium. Spectral acquisition on initiation of hydrogenation then enables the benzaldehyde → benzyl alcohol transition to be tracked. The additional presence of a broad CO stretching band of chemisorbed carbon monoxide (1852–1929 cm−1) is attributed to the hydrogen-assisted decarbonylation pathway that forms the benzene by-product.

Selective Liquid Phase Hydrogenation of Benzaldehyde to Benzyl Alcohol Over Alumina Supported Gold

We report for the first time 100% benzyl alcohol yield from the liquid phase (T = 353 K, P = 9 bar) hydrogenation of benzaldehyde over Au/Al2O3. Under the same reaction conditions, a benchmark Pt/Al2O3 catalyst promoted the formation of toluene and benzene as hydrogenolysis by-products. Reaction kinetics was subjected to a Hammett treatment and the reaction constant (ρ = 0.9) was found to be consistent with a nucleophilic mechanism. A solvent (alcohol, water and alcohol + water) effect is demonstrated and ascribed to competitive adsorption where solvation by polar (water) facilitates benzaldehyde activation.Graphic

Liquid-phase hydrogenation of benzaldehyde over Pd-Ru/C catalysts: Synergistic effect between supported metals

Bimetallic Pd-Ru/C catalysts prepared with different carbon supports were shown to be much more active in the liquid-phase hydrogenation of benzaldehyde in comparison with their monometallic analogs. In the case of systems based on nanoglobular carbon, the synergistic effect manifested itself as an increased selectivity for benzyl alcohol (86–90%) at a complete conversion of benzaldehyde, whereas the catalysts containing carbon nanotubes were highly active in hydrogenolysis of the CO bonds, which caused an increased yield of toluene (up to 56%). The synergistic effect between palladium and ruthenium in the reaction under study can be related to the changes in the electronic and dispersion state of the supported metals upon interaction with each other and formation of Pd-Ru alloy. In terms of the electronic factor, the enhanced catalytic performance of bimetallic systems can be a result of facilitation of electrophilic activation of the CO bond in benzaldehyde owing to an increased fraction of the electron-deficient palladium species. The nature of carbon support was shown to affect the electronic state of supported metals and thus catalytic properties of bimetallic Pd-Ru/C systems.

Polymers as novel modifiers for supported metal catalyst in hydrogenation of benzaldehydes

Polyethylene glycol (PEG) was impregnated on a palladium metal supported on silica gel and used in a catalyst for hydrogenation of benzaldehydes. In the vapor-phase flow reaction, the PEG modification improved catalytic activity and selectivity for a partially hydrogenated product, benzyl alcohol. In isoprene hydrogenation, selectivity for partially hydrogenated products, monoenes, was also enhanced. X-ray photoelectron spectroscopy (XPS) analysis of the modified catalysts revealed that the modification with PEG makes the palladium surface negatively charged, possibly leading to an increase in the selectivity for the partially hydrogenated product caused by enhancement of its desorption from the surface. In the liquid-phase hydrogenation of benzaldehyde, the PEG modification also increased the selectivity for benzyl alcohol.

Catalytic features of a low-temperature reduced alumina-supported platinum catalyst. Activity and selectivity in the liquid-phase hydrogenation of benzaldehyde and nitrobenzene

A low-temperature reduced (LR) supported platinum catalyst was used for the hydrogenation of benzaldehyde, nitrobenzene and their mixture in ethanol, and compared with a high-temperature reduced (HR) catalyst. For benzaldehyde the LR catalyst was highly active to the formation of benzyl alcohol and did not give benzaldehyde diethyl acetal, which was largely formed by the HR catalyst. For the mixture, benzylideneaniline was selectively produced by the LR catalyst, while the HR catalyst gave benzylaniline and the acetal.

The Influence of Reduction Methods and Conditions on the Activity of Alumina-Supported Platinum Catalysts for the Liquid Phase Hydrogenation of Benzaldehyde in Ethanol

The activities of supported metal catalysts depend on various preparation variables, including the method of reduction. A variety of reduction procedures can be applied to the preparation of supported metal catalysts. Previously, the authors used a solid-liquid reduction by sodium tetrahydroborate solution for preparing supported platinum catalysts. In this reduction, platinum precursors adsorbed on supports were brought into contact with the reducing solution. The alumina-supported platinum catalysts prepared in this way were found to display interesting activities in the liquid-phase hydrogenation of {alpha},{beta}-unsaturated aldehydes; they were highly selective to the formation of unsaturated alcohols. The selective hydrogenation of C=O bonds of {alpha},{beta}-unsaturated aldehydes is difficult to achieve with platinum catalysts without using some additives like tin and iron. The maximum temperature that the supported platinum catalysts went through was 110{degrees}C, required for the removal of water. This thermal history is a possible reason for the catalytic activity observed. Following those observations, in the present work, the authors have further examined the influence of reduction procedures by using hydrazine as well as sodium tetrahydroborate and different temperatures common during gas-phase reduction with hydrogen. The catalytic activity has been tested by the liquid-phase hydrogenation of benzaldehyde (BAL) in ethanol under mild conditions.more » 12 refs., 3 figs.« less