Function of metal oxide and complex oxide catalysts for hydrocracking of coal

Abstract

The catalytic activity and selectivity of metal oxides and complex oxides for the liquefaction of bituminous coal and lignite are reviewed first and discussed in connection with surface properties of catalysts. However, it has been realized that the functions of catalysts are not fully understood. Thus, in the present work, the hydrocracking of diphenylmethane, diphenyl ether, and benzyl phenyl ether as model compounds of coal, the dehydration of 2-propanol as a test reaction for cracking ability (acidity) of a catalyst, and the hydrogenation of naphthalene as a test reaction for hydrogenation ability of a catalyst were studied by employing various metal oxide and complex metal oxide catalysts. It has been concluded that the acidic property of a catalyst plays an important role for CC bond cleavage, while the hydrogenation ability of a catalyst is important for CO bond cleavage. This conclusion was found to be in agreement with the results of liquefaction of Akabira coal (carbon content: 83.0%) and Big Brown lignite (carbon content: 72.3%). That is, the highly acidic catalysts exhibited high activities for liquefaction of bituminous coals with high carbon content, whereas catalysts possessing high hydrogenation ability showed high activities for liquefaction of lignite containing a large amount of oxygen. The best three catalysts for Akabira coal were MoO 3Fe 2O 3SnO 2, MoO 3TiO 2, and Fe 2O 3SO 4 2-, whose activities were almost comparable to a well known MoO 3CoOAl 2O 3 catalyst, though they did not contain expensive cobalt. For Big Brown lignite, MoO 3TiO 2 was the best among the various catalysts.