Praseodymium can modify the properties of ceria (CeO2), changing the electronic structure, reducibility and catalytic behavior. Oxygen vacancies in the ceria-based samples can activate C–O and C–H bonds of small mol...Praseodymium can modify the properties of ceria (CeO2), changing the electronic structure, reducibility and catalytic behavior. Oxygen vacancies in the ceria-based samples can activate C–O and C–H bonds of small molecules such as CO2 and propane. Partially reduced Pr/CeO2-x can selectively activate C–H of propane, giving a propylene selectivity of ca. 75% at a propane conversion of 5% to 10%. Excess reduction of Pr/CeO2-x induces coking reactions during propane dehydrogenation, resulting in fast catalyst deactivation.展开更多
Due to the shortage supply of propylene and the development of shale gas,there is increased interest in on-purpose propane dehydrogenation(PDH)technology for propylene production.Ga-based catalysts have great potentia...Due to the shortage supply of propylene and the development of shale gas,there is increased interest in on-purpose propane dehydrogenation(PDH)technology for propylene production.Ga-based catalysts have great potential in PDH,due to the high activity,low carbon deposit and deactivation.Ga-hydrides formed during PDH reduce the rate,selectivity and yield of propylene.In this contribution,CO_(2)is introduced into PDH as a soft oxidant to eliminate the unfavorable intermediate species Ga^(δ+)-Hx re-generating Ga^(3+)-O pairs,and also minimize coke deposition thereby improving the catalytic performance.In situ diffuse reflectance infrared Fourier transform(DRIFT)spectroscopy experiments show that CO_(2)can effectively eliminate Ga^(δ+)-Hx.At different temperatures,co-feeding CO_(2)during PDH over Ga_(2)O_(3)/SiO_(2)catalysts with different loadings significantly improves the stability of the conversion and selectivity,especially the latter,and provide a new dimension for improving the performance of PDH process.展开更多
Solvent and kinetic isotope effects in the reaction of oxidative deamination of L-alanine, catalyzed by L-alanine dehydrogenase, AIaDH, （EC 1.4.1.1） were determined using a non-competitive spectroscopic method. The ...Solvent and kinetic isotope effects in the reaction of oxidative deamination of L-alanine, catalyzed by L-alanine dehydrogenase, AIaDH, （EC 1.4.1.1） were determined using a non-competitive spectroscopic method. The progress of the reaction was monitored spectrophotometrically by measuring the increasing absorbance of the reduced form of NADH at 340 nm. L-alanine, stereospecifically labeled with deuterium was synthesized by enzymatic reductive amination of pyruvate in presence of [（4R）-2H]-NADH, which was obtained by deuterium transfer from deuteriated formic acid to NAD~ catalyzed by FDH （formate dehydrogenase） （EC 1.2.1.2）. [2-2H]-L-alanine, the product of enzymatic synthesis catalyzed by AIaDH, was obtained with 75% deuterium enrichment and values of isotopic effects were approximated to the values corresponding to 100% of deuterium incorporation. The enzyme AIaDH isolated from Bacillus subtilis shows pro-R stereospecificity, what indicates that hydrogen is exclusively transferred from pro-R position at C-4 of the nicotinamide ring of NADH to C-2 of pyruvate to form L-alanine. Some intrinsic mechanistic details of enzymatic oxidative deamination of L-alanine were discussed using determined numerical values of kinetic and solvent isotope effects on Vmax and Vmax,│KM展开更多
文摘Praseodymium can modify the properties of ceria (CeO2), changing the electronic structure, reducibility and catalytic behavior. Oxygen vacancies in the ceria-based samples can activate C–O and C–H bonds of small molecules such as CO2 and propane. Partially reduced Pr/CeO2-x can selectively activate C–H of propane, giving a propylene selectivity of ca. 75% at a propane conversion of 5% to 10%. Excess reduction of Pr/CeO2-x induces coking reactions during propane dehydrogenation, resulting in fast catalyst deactivation.
文摘Due to the shortage supply of propylene and the development of shale gas,there is increased interest in on-purpose propane dehydrogenation(PDH)technology for propylene production.Ga-based catalysts have great potential in PDH,due to the high activity,low carbon deposit and deactivation.Ga-hydrides formed during PDH reduce the rate,selectivity and yield of propylene.In this contribution,CO_(2)is introduced into PDH as a soft oxidant to eliminate the unfavorable intermediate species Ga^(δ+)-Hx re-generating Ga^(3+)-O pairs,and also minimize coke deposition thereby improving the catalytic performance.In situ diffuse reflectance infrared Fourier transform(DRIFT)spectroscopy experiments show that CO_(2)can effectively eliminate Ga^(δ+)-Hx.At different temperatures,co-feeding CO_(2)during PDH over Ga_(2)O_(3)/SiO_(2)catalysts with different loadings significantly improves the stability of the conversion and selectivity,especially the latter,and provide a new dimension for improving the performance of PDH process.
文摘Solvent and kinetic isotope effects in the reaction of oxidative deamination of L-alanine, catalyzed by L-alanine dehydrogenase, AIaDH, （EC 1.4.1.1） were determined using a non-competitive spectroscopic method. The progress of the reaction was monitored spectrophotometrically by measuring the increasing absorbance of the reduced form of NADH at 340 nm. L-alanine, stereospecifically labeled with deuterium was synthesized by enzymatic reductive amination of pyruvate in presence of [（4R）-2H]-NADH, which was obtained by deuterium transfer from deuteriated formic acid to NAD~ catalyzed by FDH （formate dehydrogenase） （EC 1.2.1.2）. [2-2H]-L-alanine, the product of enzymatic synthesis catalyzed by AIaDH, was obtained with 75% deuterium enrichment and values of isotopic effects were approximated to the values corresponding to 100% of deuterium incorporation. The enzyme AIaDH isolated from Bacillus subtilis shows pro-R stereospecificity, what indicates that hydrogen is exclusively transferred from pro-R position at C-4 of the nicotinamide ring of NADH to C-2 of pyruvate to form L-alanine. Some intrinsic mechanistic details of enzymatic oxidative deamination of L-alanine were discussed using determined numerical values of kinetic and solvent isotope effects on Vmax and Vmax,│KM
