Influence of microwave activation on the catalytic behavior of Pd-Au/C catalysts employed in the hydrodechlorination of tetrachloromethane

Continuous 2-Methyl-3-butyn-2-ol Selective Hydrogenation on Pd/γ-Al2O3 as a Green Pathway of Vitamin A Precursor Synthesis

In this work, the effect of pretreatment conditions (10% H2/Ar flow rate 25 mL/min and 400 °C, 3 h or 600 °C, 17 h) on the catalytic performance of 1 wt.% Pd/γ-Al2O3 has been evaluated for hydrogenation of 2-methyl-3-butyn-2-ol in continuous-flow mode. Two palladium catalysts have been tested under different conditions of pressure and temperature and characterized using various physicochemical techniques. The catalytic performance of red(400 °C)-Pd/γ-Al2O3 and red(600 °C)-Pd/γ-Al2O3 are affected by the coexistence of several related factors like the competition between PdH and PdCx formation during the reaction, structure sensitivity, hydrogen spillover to the alumina support and presence or absence of Pd–Al species. High-temperature reduction leads to formation of Pd–Al species in addition to pure Pd. The Pd–Al species which reveal unique electronic properties by decreasing the Pdδ− surface concentration via electron transfer from Pd to Al, leading to a weaker Pd–Alkyl bonding, additionally assisted by the hydrogen spillover, are the sites of improved semi-hydrogenation of 2-methyl-3-butyn-2-ol towards 2-methyl-3-buten-2-ol (97%)—an important intermediate for vitamin A synthesis.

Towards High Efficacy of Pd-Au/C Catalyst for Tetrachloromethane Hydrodechlorination

We present an efficient strategy for synthesising the PdAu catalysts with a homogeneous PdAu alloy phase for environmentally important hydrodechlorination of tetrachloromethane in the gas phase. The synthesis of carbon-supported catalysts involved two major steps: (i) incorporation of palladium and gold nanoparticles into carbon support and (ii) activation of the catalysts. The critical part of this work was to find the optimal conditions for both steps. Thus, the incorporation of the nanoparticles was carried out in two ways, by impregnation and direct redox reaction method using acetone solutions of metal precursor salts. The activation was performed either by a conventional thermal reduction in hydrogen or flash irradiation in a microwave oven. The homogeneity and structure of the PdAu alloy were found to depend on the catalyst activation method critically. In all cases, we observed better homogeneity for catalysts that were subject to microwave irradiation. Moreover, the flash microwave irradiation of prepared catalysts provided catalysts of better stability and selectivity towards the desired products (hydrocarbons) in the hydrodechlorination of tetrachloromethane as compared to the catalyst obtained by conventional thermal activation in hydrogen.

Understanding Hydrodechlorination of Chloromethanes. Past and Future of the Technology

Chloromethanes are a group of volatile organic compounds that are harmful to the environment and human health. Abundant studies have verified that hydrodechlorination might be an effective treatment to remove these chlorinated pollutants. The most outstanding advantages of this technique are the moderate operating conditions used and the possibility of obtaining less hazardous valuable products. This review presents a global analysis of experimental and theoretical studies regarding the hydrodechlorination of chloromethanes. The catalysts used and their synthesis methods are summarized. Their physicochemical properties are analyzed in order to deeply understand their influence on the catalytic performance. Moreover, the main causes of the catalyst deactivation are explained, and prevention and regeneration methods are suggested. The reaction systems used and the effect of the operating conditions on the catalytic activity are also analyzed. Besides, the mechanisms and kinetics of the process at the atomic level are reviewed. Finally, a new perspective for the upgrading of chloromethanes, via hydrodechlorination, to valuable hydrocarbons for industry, such as light olefins, is discussed.

Application of silica-supported Ir and Ir-M (M = Pt, Pd, Au) catalysts for low-temperature hydrodechlorination of tetrachloromethane

Herein, it is presented a catalytic system for gas-phase hydrodechlorination of tetrachloromethane at low temperature and atmospheric pressure, using iridium supported on silica as parent catalyst. Iridium electronic configuration is suitable to catalyse the hydrodechlorination reactions, however, it has been rarely used in this reaction to date. The catalytic abilities were significantly improved when a second transition metal was added. Catalysts' stability and selectivity to the desired products (i.e. C₁-C₄ hydrocarbons) improved compared to conventional activation in hydrogen when catalysts were activated shortly with microwave irradiation. Microwave irradiation of catalysts favourably influences the homogeneity of the metallic active phase, both in terms of the size of metal crystals and the homogeneity of bimetallic systems. Addition of platinum to the 'parent' iridium catalyst improved its catalytic properties and decreased deactivation. Fresh and spent catalysts were comprehensively characterized using several techniques (BET, CO-chemisorption, XRD, XPS, electron microscopy and mass spectrometry) to determine structure-activity relationships and potential causes for catalyst deactivation. No significant changes in crystalline size or bimetallic phase composition were observed for spent catalysts (with the exception of Ir-Pd catalysts which underwent bulk carbide during the reaction).