Catalytic Dehydrogenation of Ethylbenzene in Helium and Reductive Dealkylation in Hydrogen on Nb, Mo, Ta, W, and Re Halide Clusters

Abstract

Halide clusters of [(Nb6Cl12)Cl2(H2O)4]⋅4H2O and (H3O)2[(M6Cl8)Cl6]⋅ 6H2O (M=Mo, W), which have an octahedral metal framework, and Re3Cl9, which has a triangular metal framework, developed catalytic activity for the dehydrogenation of ethylbenzene selectively to yield styrene when the halide clusters were treated in a stream of helium at 450°C. In the case of the Mo cluster, this catalytic activity appeared at 300°C. The activity increased with increasing temperature. Above 400°C, the catalytic activity decreased with time, and the selectivity for benzene increased noticeably. The reduction in the activity was caused by the formation of coke attributable to ethylene produced as a by-product. When the Nb and Ta clusters of the same structure were treated in a stream of hydrogen in the same way, no catalytic reaction proceeded. However, the Mo and W clusters in a stream of hydrogen catalyzed reductive dealkylation of ethylbenzene selectively yielding toluene and benzene. In the case of the Mo cluster, the catalytic activity appeared at 400°C, and increased with increasing temperature. The activity did not decrease with time even at high temperatures. The Re cluster, which was reduced to the metal by the treatment in hydrogen, catalyzed ring-opening degradation to yield gaseous hydrocarbons.