Effect of Gadolinium Additives on the Active Phase Morphology and Physicochemical and Catalytic Properties of MoVSbNbGdO x /SiO 2 Catalysts in the Oxidative Dehydrogenation of Ethane to Ethylene

The effect of gadolinium additives on the morphology, phase composition, and catalytic properties of MoVSbNbGdO x /SiO 2 catalysts in the oxidative dehydrogenation of ethane to ethylene (ODE) is studied. It is shown that gadolinium concentration has a significant effect on the catalytic properties. At an optimum gadolinium content (Gd/Mo = 0.01–0.015), an increase in catalytic activity and ethylene selectivity is observed: at a temperature of 400°C, the ethylene yield achieves 72%, the ethane conversion is higher than 91%, and the ethylene selectivity is higher than 79%. According to X-ray diffraction analysis and scanning and transmission electron microscopy, the main component of the catalyst is the M1 phase stabilized both in the bulk and on the surface of SiO 2 particles. The modification of the catalyst with gadolinium significantly affects the morphology of the M1 phase particles. At an optimum gadolinium content, heat treatment leads to the formation mostly of M1 phase particles with a needle-like morphology and the most developed [001] plane emerging on the surface, which exhibit the maximally high activity in ODE. The M1 phase particles with this morphology are mostly stabilized in the bulk of porous spherical SiO 2 particles; therefore, they do not undergo strong agglomeration and sintering. A smaller portion of the M1 phase particles with a plate-like morphology, which exhibit a lower catalytic activity, as well as the M2 phase particles, are stabilized on the outer surface of the SiO 2 particles. In the catalyst containing no Gd additives, M1 phase particles with a plate-like morphology are mostly formed; this factor leads to a decrease in the catalyst activity. The synthesized catalyst exhibits a long-term stable on-stream behavior in the reaction medium without a deterioration of the properties.