The influence of catalyst acid strength on the methanol to hydrocarbons (MTH) reaction

The methanol to hydrocarbons (MTH) reaction was studied over two isostructural zeotype catalysts of different acid strength, H-SAPO-5 and H-SSZ-24. Conversion of methanol alone was performed at 350-450 degrees C and WHSV = 0.31-2.48 h(-1). The product selectivities of the two catalysts were compared at similar conversion. The strongly acidic H-SSZ-24 was found to be more selective towards aromatic products and C-2-C-3 hydrocarbons as compared to the moderately acidic H-SAPO-5, which produced more non-aromatic C4+ hydrocarbons. Co-reactions of (CH3)-C-13 OH and benzene at 250-300 degrees C with low conversion of both reactants revealed that both catalysts produced ethene and propene from polymethylbenzenes via a paring mechanism. However, this reaction proceeded more readily in H-SSZ-24 than in H-SAPO-5. Furthermore, isobutene formation was found to be mainly associated with aromatic intermediates in H-SSZ-24, whereas isobutene produced over H-SAPO-5 was mainly formed via alkene intermediates. Overall, the results obtained in this study suggest that a lower acid strength promotes an alkene-mediated MTH reaction mechanism. (C) 2013 Elsevier B.V. All rights reserved.