Reaction mechanism of acetylene hydrochlorination on defective carbon supported ruthenium catalysts by DFT calculations and experimental approaches

It is critical to identify the reaction mechanism of carbon supported metal catalysts for the exploration of high-performance catalyst in acetylene hydrochlorination. Herein, we reported a systematically study on the...

Co/Ba/La2O3 catalyst for ammonia synthesis under mild reaction conditions

Ruthenium catalysts may allow realization of renewable energy–based ammonia synthesis processes using mild reaction conditions (<400 °C, <10 MPa). However, ruthenium is relatively rare and therefore expensive. Here, we report a Co nanoparticle catalyst loaded on a basic Ba/La2O3 support and pre-reduced at 700 °C (Co/Ba/La2O3_700red) that showed higher ammonia synthesis activity at 350 °C and 1.0–3.0 MPa than two benchmark Ru catalysts, Cs+/Ru/MgO and Ru/CeO2. The synthesis rate of the catalyst at 350 °C and 1.0 MPa (19.3 mmol h−1g−1) was 8.0 times that of Co/Ba/La2O3_500red and 6.9 times that of Co/La2O3_700red. The catalyst showed activity at temperatures down to 200 °C. High-temperature reduction induced formation of a BaO-La2O3 nano-fraction around the Co nanoparticles, which increased turnover frequency, inhibited Co nanoparticle sintering, and suppressed ammonia poisoning. These strategies may also be appliable to nickel catalysts.

Reductive Catalytic Fractionation of Lignocellulosic Biomass: A New Promising Method of its Integrated Processing

The review discusses the results of recent studies in the promising field of integrated processing of lignocellulosic biomass – the reductive catalytic fractionation (RCF). The effect of catalysts, cocatalysts, solvents, hydrogen sources and features of lignocellulosic feedstock on the selectivity of monomeric products formation from lignin is considered. RCF processes are performed mostly with the heterogeneous catalysts, which allow implementing the reductive depolymerization of lignin to obtain low-molecular compounds and preserve carbohydrate components of biomass. Among the studied catalysts based on platinum group metals and transition metals, the highest activity is observed for the catalysts containing Pd, Pt, Ru and Ni. Features of the metal also affect the composition of the resulting products. Thus, ruthenium catalysts make it possible to obtain 4-propylguaiacol as the main product, while Ni and Pd – 4-propanolguaiacol. Mo-containing catalysts, owing to their lower hydrogenating activity, can be used to obtain monolignols or their etherified derivatives with the preservation of carbohydrate components of lignocellulosic biomass. However, most efficient in RCF processes are the bifunctional catalysts, which have both the acidic and metallic active sites. Acidic sites promote the cleavage of the ether β-O-4 bonds, whereas metallic sites – the reduction of the formed intermediate compounds. An important aspect of choosing the appropriate catalysts for RCF process is the possibility of their repeated application. The use of a ferromagnetic catalyst or a catalyst basket allows separating the catalyst from the products.

Unexpected reactivity related to support effects during xylose hydrogenation over ruthenium catalysts

Xylose is a major component of hemicelluloses. In this paper, its hydrogenation to xylitol in aqueous medium was investigated with two Ru/TiO2 catalysts prepared with two commercial TiO2 supports. A strong impact of support on catalytic performances was evidenced. Ru/TiO2-R led to fast and selective conversion of xylose (100 % conversion in 2 h at 120°C with 99 % selectivity) whereas Ru/TiO2-A gave a slower and much less selective transformation (58 % conversion in 4 h at 120°C with 17 % selectivity) with the formation of several by-products. Detailed characterization of catalysts with ICP, XRD, FTIR, TEM, H2 chemisorption, N2 porosimetry, TPR and acid-base titration were performed to elucidate the role of each support. TiO2-R has a small specific surface area with large ruthenium nanoparticles in weak interaction with TiO2 support and no acidity, whereas TiO2-A is a mesoporous material with a large specific surface area, mildly acidic, and bears small ruthenium particles in strong interaction with TiO2 support. The former was very active and selective for xylose hydrogenation to xylitol whereas the latter was less active and poorly selective. Moreover, careful analysis of reaction products also revealed that TiO2 anatase can catalyze undesired side-reactions such as xylose isomerisation to various pentoses, and therefore the corresponding unexpected polyols (arabitol, ribitol) were produced during xylose conversion by hydrogenation. In a first approach of the kinetics, a simplified kinetic model was built to compare quantitatively intrinsic reaction rates of both catalysts. The kinetic constant for hydrogenation was 20 times higher for Ru/TiO2-R at 120°C.

Synthesis of ruthenium catalysts with chiral arene ligand derived from natural camphor

Ruthenium complex with chiral arene ligand [(camphor-arene)RuCl2]2 was synthesized by the reaction of RuCl3∙nH2O with the chiral diene, which was obtained from natural camphor in 3 steps. This complex catalyzed asymmetric hydrogenation of acetophenone (64-85% ee), but decomposed in the catalytic reactions involving C-H activation of 2-phenyl-pyridine or benzoic acid derivatives.