ABSTRACT
The fundamental role of the carbon carrier Sibunit® in the formation of active and selective phases in low-percentage Pt-containing catalysts Pt/C, Pt/Ni/C, Pt/Ni-Cr/C for the complete dehydrogenation of bicyclohexyl into biphenyl (320 °C, 1 atm) is shown. The Pt/Ni-Cr/C catalyst showed the greatest activity and selectivity in the complete dehydrogenation of bicyclohexyl into biphenyl. Detailed analysis of the catalyst surface by XPS, TEM-HR and EDX methods revealed two main processes associated with the high activity and successful course of the reaction of bicyclohexyl dehydrogenation: the formation of an active carbide Pt1-xCx phase and graphitization of the carbon carrier. Both these processes are realized equally in the Pt/Ni-Cr/C catalyst demonstrating the highest activity. The formation of the Pt1-xCx carbide phase at a low extent of graphitization of the catalyst surface is predominant for the Pt/C catalyst. Graphitization of the carbon carrier is most pronounced for Pt/Ni/C, where the yield of biphenyl is significantly reduced. The formation of graphite for the Pt/Ni/C catalyst at the metal-carrier interface leads to the encapsulation of a metal particle in a graphite shell, which apparently determines its low activity in the conversion of bicyclohexyl.
ABSTRACT
Hydrogenation of phenol in aqueous solutions on Pt-Ni/SiO2, Pt-Ni-Cr/Al2O3, Pt/C, and Ru/C catalysts was studied at temperatures of 150-250 °C and pressures of 40-80 bar. The possibility of hydrogenation of hydrolysis lignin in an aqueous medium in the presence of a Ru/C catalyst is shown. The conversion of hydrolysis lignin and water-soluble sodium lignosulfonate occurs with the formation of a complex mixture of monomeric products: a number of phenols, products of their catalytic hydrogenation (cyclohexanol and cyclohexanone), and hydrogenolysis products (cyclic and aliphatic C2-C7 hydrocarbons).
ABSTRACT
Reduction of CO2 with hydrogen into CO was studied for the first time on alumina-supported Co and Fe catalysts under supercritical conditions with the goal to produce either CO or CH4 as the target products. The extremely high selectivity towards methanation close to 100% was found for the Co/Al2O3 catalyst, whereas the Fe/Al2O3 system demonstrates a predominance of hydrogenation to CO with noticeable formation of ethane (up to 15%). The space-time yield can be increased by an order of magnitude by using the supercritical conditions as compared to the gas-phase reactions. Differences in the crystallographic phase features of Fe-containing catalysts cause the reverse water gas shift reaction to form carbon monoxide, whereas the reduced iron phases initiate the Fischer-Tropsch reaction to produce a mixture of hydrocarbons. Direct methanation occurs selectively on Co catalysts. No methanol formation was observed on the studied Fe- and Co-containing catalysts.
