Study of the preparation and catalytic performance of molybdenum carbide catalysts prepared with C_2H_2/H_2 carburizing mixture

摘要

A series of molybdenum carbide catalysts were prepared using 10% C_2H_2/H_2 to carburize molybdenum trioxide at different temperatures. Their catalytic performance was evaluated using methane partial oxidation to synthesis gas as the model reaction. The structure of the catalysts treated under various conditions was characterized using X-ray diffraction, laser Raman spectroscopy, and scanning electron microscopy. The results show that MoO_3 is first converted into MoO_2 and MoC_(1-x). With the rise of the carburization temperature, MoO_2 is converted into MoC_(1-x) and the catalyst crystallites tend to be very small. However, the catalyst surface remains coated by MoO_3 or MoO_2. When the carbides are heated in N_2 to 850 deg C, they are converted into MoC_(1-x) and beta-Mo_2C. Interestingly, all the catalyst samples show high CH_4 conversion and CO selectivity in partial oxidation of methane, although the pretreatment has some effect on the preliminary activity and selectivity. The catalyst is partly oxidized and there is a small amount of carbon deposition after the activity test. Acetylene is therefore a good carburizing agent for preparing molybdenum carbide catalyst at low temperature for the partial oxidation of methane.