Comparative catalytic study on butene/isobutane alkylation over LaX and CeX zeolites: The influence of calcination atmosphere

Lanthanum-containing (LaX) and cerium-containing X zeolites (CeX) were prepared by a double-exchange, double-calcination method. By changing the calcination atmospheres between nitrogen and air, the Ce-IV contents in CeX zeolites were adjusted and their impacts on physicochemical properties and catalytic performance in isobutane alkylation were established. The crystallinity of CeX zeolite was found to be negatively correlated with the Ce-IV content. This is believed to be due to the water formed during the oxidation of Ce-III, which facilitates the framework dealumination. As a consequence, calcining in air resulted in a great elimination of strong Bronsted acid sites while under nitrogen protection, this phenomenon was mostly hindered and the sample's acidity was preserved. When tested in a continuously flowed slurry reactor, the catalyst lifetime for isobutane alkylation was found to be linearly related to the strong Bronsted acid concentration. In addition, Ce3+ was found more benefit for the hydride transfer compared with La3+, which is ascribed to the stronger polarization effect on the CH bond of isobutane. Moreover, the decline of hydride transfer activity can be slowed down by the catalytic cracking of the bulky molecules. Based on the product distribution, a new catalytic cycle of dimethylhexanes (DMHs) involving a direct formation of isobutene rather than tert-butyl carbocation was proposed in isobutane alkylation. (C) 2021 Chemical Industry and Engineering Society of China (CIESC) and Chemical Industry Press (CIP) Published by Elsevier B.V. All rights reserved.

Automated summary

The physicochemical properties and catalytic performance of CeX zeolites in isobutane alkylation were investigated by adjusting the Ce-IV content through changing the calcination atmospheres. The crystallinity of CeX zeolite was found to be negatively correlated with the Ce-IV content. The elimination of strong Bronsted acid sites was influenced by the calcination atmospheres, resulting in different acidity levels.