Synthesis of tungsten carbide on Al-SBA-15 mesoporous materials by carburization

Abstract

Aluminum was incorporated into SBA-15 supports at molar ratios Si/Al = 10 and 2 by the pH-adjusting method. The calcined mesoporous Al-SBA-15 supports, as well as the Al-free SBA-15 support, were impregnated with ammonium paratungstate ((NH4)10·[H2W12O42]·4H2O) aqueous solution. Tungsten carbide (W2C) was synthesized by temperature programmed carburization (TPC) from the WO3 supported on Al-SBA-15 and SBA-15 in a flow of CH4/H2. These resultant materials were characterized by powder X-ray diffraction (XRD), N2 adsorption/desorption, 27Al NMR and Raman spectroscopies, and transmission electron microscopies (TEM and HRTEM). W2C species were obtained after the carburization process in all the materials. The mesoporous structure of the SBA-15 supports was preserved at all synthesis steps. XRD and TEM analyses revealed that the introduction of aluminum species into the SBA-15 greatly enhanced the dispersion of WO3 and W2C phases during the calcination and carburization steps, respectively. In situ XRD measured during the carburization in a synchrotron facility provided further details of the reduction of tungsten trioxide species as a function of temperature. The presence of aluminum in the SBA-15 notably affected the distribution and the reduction temperature of the tungsten oxide species.