Selective Synthesis of Methylnaphthalenes in HSAPO-34 Cages and Their Function as Reaction Centers in Methanol-to-Olefin Catalysis

Abstract

Several recent papers have demonstrated that the conversion of methanol to olefins on the silico-aluminophosphate solid acid catalyst HSAPO-34 usually requires methylbenzenes that function as scaffolds (reaction centers) for carbon−carbon bond making and breaking steps. These benzene rings form in the ca. 1 nm cages through ship-in-a-bottle routes from olefins, and they cannot exit the ca. 0.38 nm windows connecting cages. Here, we report a procedure for the selective (80%) synthesis of naphthalene in the cages of HSAPO-34 based on methanol conversion at 600 °C. These naphthalene molecules are accessible to methanol and react at 400 °C to form methylnaphthalenes in the cages with up to four methyl groups. We find that HSAPO-34 catalysts with methylnaphthalenes as the primary entrained hydrocarbon species eliminate ethylene and propene, much like methylbenzenes. A careful comparison of catalysts prepared with either methylnaphthalenes or methylbenzenes showed the former to be ca. one-third as active as the latter (for comparable numbers of reaction centers), but the methylnaphthalene-based catalysts yielded higher ethylene selectivity (at comparable conversions) than the methylbenzene-based catalysts.