Side-chain alkylation of toluene with methanol over boron phosphate modified cesium ion-exchanged zeolite X catalysts

A series of boron phosphate (BPO₄) modified ion-exchanged CsX zeolites, prepared by impregnation method, were characterized by a variety of means and utilized as catalysts for the side-chain alkylation of toluene with methanol. Both BPO₄ and Cs species are highly dispersed on the surface/channel of the BPO₄/CsX zeolites. The addition of a small amount of BPO₄ has no obvious effect on the basic strength of catalysts, but decreases the number of basic sites slightly. Meanwhile, more weak Lewis acidic sites appear with the increasing BPO₄ loading. Compared with CsX, the BPO₄ modified CsX catalysts exhibit lower ability for the adsorption/activation of methanol to produce surface intermediates like formaldehyde, unidentate formate and bidentate formate. Catalytic reaction results showed that modification of CsX with boron phosphate can improve both the conversion of toluene and the selectivity of styrene. The inhibition role in producing the unfavorable bidentate formate might be a key factor for finally resulting in the improvement of the catalytic properties of BPO₄/CsX catalysts for the side-chain alkylation of toluene with methanol.