Olefin Oligomerization by Main Group Ga3+ and Zn2+ Single Site Catalysts

Abstract

In heterogeneous catalysis, olefin oligomerization is typically performed on immobilized transition metal ions, such as Ni2+ and Cr3+. Here we report that silica-supported, single site catalysts containing immobilized, main group Zn2+ and Ga3+ ions catalyze ethylene and propylene oligomerization to an equilibrium distribution of linear olefins with rates similar to that of Ni2+. The molecular weight distribution of products formed on Zn2+ is similar to Ni2+; while Ga3+ forms higher molecular weight olefins. In situ spectroscopic and computational studies suggest that oligomerization unexpectedly occurs by the Cossee-Arlman mechanism via metal hydride and metal alkyl intermediates formed during olefin insertion and β-hydride elimination elementary steps. Initiation of the catalytic cycle is proposed to occur by heterolytic C-H dissociation of ethylene, which occurs at about 250°C where oligomerization is catalytically relevant. This work reports new chemistry for main group metal catalysts with potential for development of new olefin processes.

A Molecular Analogue of the C−H Activation Intermediate of the Silica‐Supported Ga(III) Single‐Site Propane Dehydrogenation Catalyst: Structure and XANES Signature

“…However, this system undergoes rapid deactivation likely due to the reduction of Ga 2 O 3 [6–12] . While Ga 2 O 3 ‐based materials readily deactivate and cannot be used on industrial scales for PDH, the corresponding Ga‐zeotype catalysts are used to convert propane into aromatics in the commercial Cyclar © process; this process is proposed to also involve propane dehydrogenation as a key step on isolated Ga sites before the further conversion of propene to aromatics on acid sites [13–16] . These unique catalytic properties have led to the synthesis of isolated Ga sites at the surface of non‐reducible bulk materials such as silica to generate stable propane dehydrogenation catalysts [17–19] …”