“Ab initio” synthesis of zeolites for preestablished catalytic reactions

Abstract

Unlike homogeneous catalysts that are often designed for particular reactions, zeolites are heterogeneous catalysts that are explored and optimized in a heuristic fashion. We present a methodology for synthesizing active and selective zeolites by using organic structure-directing agents that mimic the transition state (TS) of preestablished reactions to be catalyzed. In these zeolites, the pores and cavities could be generated approaching a molecular-recognition pattern. For disproportionation of toluene and isomerization of ethylbenzene into xylenes, the TSs are larger than the reaction products. Zeolite ITQ-27 showed high disproportionation activity, and ITQ-64 showed high selectivity for the desired para and ortho isomers. For the case of a product and TS of similar size, we synthesized a catalyst, MIT-1, for the isomerization of -dicyclopentane into adamantane.

Building Zeolites from Precrystallized Units: Nanoscale Architecture

“…[5] Nevertheless,b yu sing semiempirical routes it is possible for scientists to synthesize zeolite frameworks with particular physicochemical properties,such as pore topologies or crystal sizes. [7] Theintroduction of organic cations has greatly expanded the possibilities in zeolite synthesis,a nd many efforts have been devoted to design families of organic molecules as organic structure-directing agents (OSDAs). [7] Theintroduction of organic cations has greatly expanded the possibilities in zeolite synthesis,a nd many efforts have been devoted to design families of organic molecules as organic structure-directing agents (OSDAs).…”

Electrophilic aromatic substitution over zeolites generates Wheland-type reaction intermediates

“…Moreover, two different types of zeolite-trapped organic species were identified (mobile and rigid). Knowledge of such mobility-dependent features of surface-trapped organics in heterogeneous catalysis will not only be useful for the development of superior and/or upgraded catalyst materials for the EB reaction (via designing zeolite catalysts to mimic transition states of reactions) 9 , but also contribute to the basic understanding of zeolitecatalysed hydrocarbon conversion chemistry.…”

“…Despite these industrial advancements, there are surprisingly no detailed studies discussing the S E Ar reaction mechanism of the zeolite-catalysed EB processes. The importance of mechanistic understanding of this industrially relevant reaction cannot be ignored, as such information is crucial to maximizing yields, reducing costs and minimizing waste in order to increase economic value 9 . Furthermore, this reaction is also of academic interest, as the underlying mechanistic principles of S E Ar are currently the subject of debate.…”

Preferential Siting of Aluminum Heteroatoms in the Zeolite Catalyst Al‐SSZ‐70

“…[10] Fora s-synthesized zeolites containing organic structure-directing agents (OSDAs) that drive preferential configurations of heteroatom sites,i nformation on framework heteroatom distributions may be extracted by the refinement of synchrotron Xray diffraction data. [11,[15][16][17] Herein, analyses of solid-state two-dimensional (2D) NMR spectra with complementary synchrotron X-ray powder diffraction analyses establish the preferential siting of Al heteroatoms in calcined zeolite Al-SSZ-70. [11,[15][16][17] Herein, analyses of solid-state two-dimensional (2D) NMR spectra with complementary synchrotron X-ray powder diffraction analyses establish the preferential siting of Al heteroatoms in calcined zeolite Al-SSZ-70.…”