Selective synthesis of methylnaphthalenes in HSAPO-34 cages and their function as reaction centers in methanol-to-olefin catalysis

Several recent papers have demonstrated that the conversion of methanol to olefins on the silicoaluminophosphate 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 600degreesC. These naphthalene molecules are accessible to methanol and react at 400degreesC to form methylnaphthalenes in the cages with up to four methyl groups. We find that HSAPO-34 catalysts with methylnaphthatenes 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 methlnaphthalene-based catalysts yielded higher ethylene selectivity (at comparable conversions) than the methylbenzene-based catalysts.