Thermogravimetric study of nickel-containing zeolites deactivated in glucose conversion

Abstract

Heterogeneous catalytic conversion of carbohydrates in order to obtain platform- substances over acid catalysts is an important modern area of research. However, today the problem of deactivation of solid catalysts in these processes is poorly understood. The aim of the work was thermogravimetric study of nickel-containing (5% wt.) hydrogen forms of zeolites Y, ZSM-5 and M deactivated in glucose dehydration. The peculiarities of two processes, including endothermic process of dehydration and the exothermic process of carbonaceous deposits combustion, were investigated by the method of ther-mogravimetry. The latter on the DTA curves is represented by two (three) exothermic maxima in the temperature range of 325-450 oC. Among the studied samples only for zeolite Y there is a phase transi-tion without mass change in the range of 900-1000 oC. The mass loss of the samples due to dehydra-tion and combustion of coke is 30, 20 and 15% for NiHY, NiHM and NiHZSM-5, respectively, of which carbonaceous deposits account for 18, 10 and 10% of the mass. A similar rate of dehydration and burnout of deposits was observed in the case of catalysts based on wide-porous zeolites, as well as a lower rate of burnout in the case of medium-porous zeolite ZSM-5. The calculated activation energy of deposition combustion, which is 25-50 kJ/mol, is caused by the proceeding of low-temperature oxi-dation catalyzed by nickel-containing zeolites. It was found that the bulk of coke deposits burns up to 450 oC, which indicates the formation of only coke precursors, which, apparently, are humin com-pounds. They do not undergo further processes of transformation and compaction.