MoVTeNb mixed oxide is a highly active and selective catalyst for oxidative dehydrogenation of ethane to produce ethylene, which exhibits the so-called M1 and M2 crystalline phases. Thermal stability of MoVTeNb catalytic system was assessed under reactions conditions, for this end the catalyst was exposed to several reaction temperatures spanned from 440 to 550°C and the pristine and spent materials were thoroughly analyzed by several characterization techniques. The catalyst's stability limit to operate at reactions temperatures <500°C, since, when reaction temperature is ≥500°C brings about the removal of tellurium from the intercalated framework channels of M1 crystalline phase. Rietveld refinement of XRD patterns and microscopies results point out that the tellurium loss cause the progressive partial destruction of M1 phase, thus decreasing the active sites amount and forming a MoO 2 crystalline phase, which is inactive in the employed reactions conditions. Raman spectroscopy confirms the MoO 2 phase development in function of reaction temperature. From HRTEM and EDS analyses it was noticed that tellurium depart occurs preferentially from the end sides of the needle-like M1 crystals, across the [001] plane. A detailed analysis of the solid deposited at the reactor outlet displays that it consists mainly in metallic tellurium; hence, the tellurium detaching is carried out by means of a reduction process of Te 4+ to Te 0 due to a combination of reaction temperature and feed composition. In order to keep the catalytic performance exhibited by MoVTeNb mixed oxide, hot spots along the reactor bed should be avoided or controlled for maintaining the catalytic bed temperature <500°C.

A MoVTeNb multimetallic mixed oxide was studied for the oxidative dehydrogenation of ethane, a promising alternative for catalytic ethylene production. Lab-scale steady-state experimental reaction data were obtained according to a 3 k experimental design to investigate the simultaneous effect of temperature (400−480 °C) and space−time [23−70 g cat h (mol of ethane) −1 ]. A fixed-bed reactor at atmospheric pressure was employed, feeding a mixture of ethane, oxygen, and nitrogen. Ethane conversion varied from 17 to 85%, whereas selectivity for ethylene and CO x varied from 94 to 76% and from 4.0 to 24%, respectively. These types of analyses are useful for determining the optimum reaction conditions to enhance the catalytic performance of the mixed oxides presented herein.

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ElsevierQuintana-Solorzano, R.; Barragan-Rodriguez, G.; Armendariz-Herrera, H.; López Nieto, JM.; Valente, JS. (2014). Understanding the kinetic behavior of a Mo-V-Te-Nb mixed oxide in the oxydehydrogenation of ethane. Fuel. 138:15-26. doi:10.1016Fuel. 138:15-26. doi:10. /j.fuel.2014

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