from first principles PP-I-1

PP-IV-23On the Role of Mass-Transfer Processes in the Overall Kineticsof the Three-Phase Glucose Oxidation into Gluconic Acidover Pd, Au and PdAu CatalystsTaran O.P. 1,2 , Delidovich I.V. 1 , Gromov N.V. 1,3 , Parmon V.N. 1,31 Boreskov Institute of Catalysis SB RAS, Novosibirsk, Russia2 Novosibirsk State Technical University, Novosibirsk, Russia3 Novosibirsk State University, Novosibirsk, Russiaoxanap@catalysis.ruThe biomass of green plants contains ca. 75% carbohydrates which are the main source of therenewables employed for the production of bio-based products. One of these products isgluconic acid which is widely used in industry. Nanosized supported Au, Pd, and PdAucatalysts are known to be the best catalysts for the glucose oxidation. However, efficiency ofheterogeneous catalytic processes in multiphase medium depends not only on an intrinsiccatalytic activity but also on mass-transfer phenomena.The aim of this work is a study of the mass-transfer impact on the apparent reaction rate of theglucose oxidation process over the Au, Pd and PdAu catalysts supported on C and Al 2 O 3 . Thecatalysts with the different active components and their morphology, hydrophobicity werechosen in order to evaluate the influence of these factors on the overall kinetics.The rates of the gas-liquid and liquid-solid oxygen transfer were calculated and compared withthe apparent reaction rate of the glucose oxidation. For estimation of the effectiveness factor of thecatalyst grain the Weisz modulus was calculated. The influence of the mass transfer of oxygen onthe overall kinetics was analyzed under different regimes of the process.The catalysts on alumina demonstrated the higher catalytic activity than the samples on carbon atthe same dispersity of the supported metals at high Glu:Au molar ratios. High effectiveness of thecatalysts (>95%) was found for the Au/Al 2 O 3 with a uniform distribution of Au in support grainsas well as for the Pd/C catalysts with an egg-shell distribution of the noble metal. Theeffectiveness factor of Au/C grains was estimated to be 60-70% which implies pore-diffusionlimitation of reaction due to uneven distribution of Au nanoparticles in the grains of catalysts.At low Glu:Au molar ratios (large amount of catalysts), when the oxidation process is limitedby the oxygen gas-liquid transfer, the apparent rate of the glucose oxidation over the carbonsupportedcatalysts is higher than over the alumina-supported ones. This phenomenon can beexplained by a high adhesion between oxygen and hydrophobic carbon facilitating thegas-liquid-solid oxygen transfer.308