Study of the Tungstated Alumina Catalysts Deactivation in the Process of Sorbitol Hydrodeoxygenation and Their Regeneration Efficiency Evaluation

摘要

The properties of catalysts based on tungstated aluminum oxide (WA) with different nature and content of the supported metal (Pt, Pd, Rh, Ru, Ni) in sorbitol hydrodeoxygenation in flow mode at 653 K, 4.0 MPa, weight hourly space velocity (WHSV) of raw materials 1.0 h~(-1) for 8 hours were studied. The samples were characterized by N2 physical adsorption, H2-TPR, CO chemisorption, TEM, NH_3-TPD, XRD and DTA-DTG techniques. On all catalysts, a complete transformation of the substrate is observed with the formation of C_5-C_7 hydrocarbons as main products, which include nalkanes, cycloalkanes and iso-alkanes. After 1 h of reaction, the yield of C_5-C_7 alkanes increases from 42 to 74 mol. % in the series of catalysts: 5-Ni/WA < 0.5-Ru/WA < 0.5-Pd/WA < 0.5-Rh/WA < 0.5-Pt/WA. The value of the research octane number (RON) of the C_5-C_7 fraction increases from 62 to 80 in the series of samples: 0.5-Pt/WA < 0.5-Pd/WA < 0.5-Rh/WA < 5-Ni/WA < 0.5-Ru/WA. Stable values yield and RON C_5-C_7 fractions (not less than 57.1 mol.% and 70 points, respectively) are achieved on 0.5-Pd/WA catalyst for 8 hours. The main causes of deactivation of all WA-supported catalysts include the formation of carbonaceous deposits and phase transformations of the support in hydrothermal conditions. Oxidative regeneration at a temperature of 973 K contributes to the restoration of textural properties and phase composition of deactivated catalysts. The reduction of the regenerated catalysts at 773 K does not ensure the complete restoration of their dispersion and acidity. For 0.5-Pd/WA catalyst, which is the most stable in hydrodeoxygenation of the sorbitol, the smallest decrease in acidity and dispersion of the supported metal after oxidative regeneration and reduction is observed. The use of methods for the re-dispersion of particles of supported palladium will increase the efficiency of this catalyst.