Skeletal isomerization of 1-butene on WO x/γ-Al 2O 3

Abstract

The catalytic behavior of WO x /γ-Al 2O 3 (having different tungsten loading) during the 1-butene skeletal isomerization at 380°C, atmospheric pressure, and 0.15 atm 1-butene partial pressure was measured. Catalysts were prepared by impregnation using an equilibrium–adsorption technique, being characterized by specific surface area and cumulative pore volume measurements, temperature-programmed reduction (TPR), ammonia temperature-programmed desorption (NH 3-TPD), X-ray photoelectron spectroscopy (XPS), laser Raman spectroscopy (LRS), and microcalorimetric measurements. After a standard calcination procedure the isobutene production (which was practically constant with time-on-stream) reached a maximum when increasing the tungsten loading. After 240 min of reaction the catalytic bed showed two layers: the upper part of the bed is completely black and the bottom is light brown. By modifying the calcination conditions, the isobutene production is decreased with time and the catalyst finished completely black all along the bed. Temperature-programmed oxidation (TPO) analysis indicated that the coke deposited during the reaction burns at high temperature independently of both tungsten loading and calcination conditions, mainly differing in the total amount. Product distribution shows the absence of C 1 and C 2 and a C 3/C 5 ratio of practically one; then it can be considered that C 8 intermediate species are formed. According to these data, deactivation could take place from a common intermediate, which can either desorb isobutene or produce coke, in a parallel-type deactivation mechanism.