1 research outputs found
Chemical, Structural, and Morphological Changes of a MoVTeNb Catalyst during Oxidative Dehydrogenation of Ethane
MoVTeNb mixed oxide, a highly active and
selective catalyst for the oxidative dehydrogenation of ethane to
produce ethylene, exhibits the so-called M1 and M2 crystalline
phases. The thermal stability of the MoVTeNb catalytic system
was assessed under varying reaction conditions; to this end, the
catalyst was exposed to several reaction temperatures spanning
from 440 to 550 °C. Both the pristine and spent materials were
analyzed by several characterization techniques. The catalyst
was stable below 500 °C; a reaction temperature of ≥500 °C
brings about the removal of tellurium from the intercalated
framework channels of the M1 crystalline phase. Rietveld
refinement of X-ray diffraction patterns and microscopy results showed that the tellurium loss causes the progressive partial
destruction of the M1 phase, thus decreasing the number of active sites and forming a MoO2 crystalline phase, which is inactive
for this reaction. Raman spectroscopy confirmed the MoO2 phase development as a function of reaction temperature. From highresolution
transmission electron microscopy and energy-dispersive X-ray spectroscopy analyses it was noticed that tellurium
departure occurs preferentially from the end sides of the needlelike M1 crystals, across the [001] plane. Detailed analysis of a
solid deposited at the reactor outlet showrf that it consisted mainly of metallic tellurium, suggesting that the tellurium
detachment occurs via reduction of Te4+ to Te0 due to a combination of reaction temperature and feed composition. Thus, in
order to sustain the catalytic performance exhibited by MoVTeNb mixed oxide, hot spots along the reactor bed should be
avoided or controlled, maintaining the catalytic bed temperature below 500 °C.This work was financially supported by the Instituto Mexicano del Petroleo.Valente, JS.; Armendariz-Herrera, H.; Quintana-Solorzano, R.; Del Angel, P.; Nava, N.; Masso RamĂrez, A.; LĂłpez Nieto, JM. (2014). Chemical, Structural, and Morphological Changes of a MoVTeNb Catalyst during Oxidative Dehydrogenation of Ethane. ACS Catalysis. 4:1292-1301. doi:10.1021/cs500143jS12921301