Skeletal isomerization of 1-butene on WOx/gamma-Al2O3

The catalytic behavior of WOx/gamma-Al2O3 (having different tungsten loadin g) during the 1-butene skeletal isomerization at 380 degrees C, atmospheric pressure, and 0.15 atm 1-butene partial pressure was measured. Catalysts w ere prepared by impregnation using an equilibrium-adsorption technique, bei ng characterized by specific surface area and cumulative pore volume measur ements, temperature-programmed reduction (TPR), ammonia temperature-program med desorption (NH3-TPD), X-ray photoelectron spectroscopy (XPS), laser Ram an spectroscopy (LRS), and microcalorimetric measurements. After a standard calcination procedure the isobutene production (which was practically cons tant with time-on-stream) reached a maximum when increasing the tungsten lo ading. After 240 min of reaction the catalytic bed showed two layers: the u pper 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. Te mperature-programmed oxidation (TPO) analysis indicated that the coke depos ited during the reaction burns at high temperature independently of both tu ngsten loading and calcination conditions, mainly differing in the total am ount. Product distribution shows the absence of C-1 and C-2 and a C-3/C-5 r atio of practically one; then it can be considered that Cg intermediate spe cies are formed. According to these data, deactivation could take place fro m a common intermediate, which can either desorb isobutene or produce coke, in a parallel-type deactivation mechanism. (C) 1999 Elsevier Science B.V. All rights reserved.