Steam reforming of guaiacol over Ni/SiO_2 catalyst modified with basic oxides: Impacts of alkalinity on properties of coke

摘要

Alkalinity is an important parameter affecting adsorption and evolution of reaction substrates in steam reforming reactions. In this study, steam reforming of guaiacol, a model compounds in the volatiles in gasification of biomass, over Ni/SiO2 modified with Na, Mg or La was investigated. The results showed that the strong alkalinity induced by Na or Mg addition to Ni/SiO2 led to remarkably decreased catalytic activity. The high alkalinity also promoted formation and accumulation of the oxygen-containing species such as CO*, C-O-C aliphatic structure and carbonyl functionalities, which were precursors of the polymeric products with big pi-conjugated structures and coke. La addition increased the alkalinity to a mild extent and promoted the nickel dispersion, enhancing the catalytic activity and the resistivity towards coking. The formation of the thermally stable amorphous coke in the Na or Mg modified catalyst wrapped nickel sites and led to rapid catalyst deactivation. Both amorphous form and in carbon nanotube form of coke defective structures were formed over LaNi/SiO2 and Ni/SiO2 catalysts, resulting from the distinct reaction intermediates formed during the steam reforming of guaiacol.