Ga(Nb,Ta)SiBEA zeolites prepared by two-step postsynthesis method: acid-base characteristics and catalytic performance in the dehydrogenation of propane to propylene with CO_2

摘要

Ga(Ta,Nb)SiBEA zeolites with Ta(V), Nb(V) and Ga(III)-single sites were prepared by two-step post-synthesis preparation procedure as evidenced by X-ray Diffraction, Fourier Transform Infrared Spectroscopy (FT-IR), Ga-71 Magic Angle Spinning Nuclear Magnetic Resonance Spectroscopy and X-ray Photoelectron Spectroscopy. The acid-base properties of the zeolite catalysts were studied by Temperature-Programmed Desorption of NH3 and CO2 with mass-spectrometry control and FT-IR spectroscopy of adsorbed pyridine. The catalytic performance of the Ga(Ta,Nb)SiBEA was tested in the process of oxidative dehydrogenation of propane to propylene with CO2. For Ga(4.0)SiBEA zeolite catalyst the propane conversion of 57.5% and propene selectivity of 64-73% at 873 K was achieved. For Ga-1.0-, Ga2.0Ta2.0- and Ga(2.0)Nb(2.0)SiBEA catalysts a higher propylene selectivity of 70-77% was reached. The key role of weak and medium strength Lewis acid sites related to the presence of well dispersed framework Ga(III) was determined for the target process.