Elucidating the Distribution and Speciation of Boron and Cesium in BCsX Zeolite Catalysts for Styrene Production

Abstract

An improved understanding of the nature and distribution of boron and cesium species in BCsX zeolites is a prerequisite to guide future developments in the environmentally attractive, yet challenging, production of styrene through the side-chain alkylation of toluene with methanol. Herein, standard characterization and catalytic tests are complemented by integrated visualization through time-of-flight secondary-ion mass spectrometry and energy-dispersive X-ray spectroscopy and detailed assessment by Cs and B NMR spectroscopy, to correlate the properties and performance during successive ion-exchange and impregnation steps in the preparation of both powders and millimeter-sized granules. The results highlight a significant impact of catalyst scaleup on the effective introduction of boron species, which originates chemical heterogeneity that is linked to selectivity losses. They also illustrate the complexity of elucidating the role of this promotor, which interacts with cesium cations and exhibits different coordination states and chemical environments, depending on the pretreatment.

Supramolecular Organization in Confined Nanospaces

“…The change of B coordination from tetrahedral to trigonal leads to interruptions in the framework and is accompanied by a 10 ppm downfield shift of 11 B NMR signal,, whereas tetrahedral boron geometry is recovered upon hydration . Such weaker Brønsted acidity of B‐sites guarantees a high selectivity for ethylene from methane and is relevant for the environmentally friendly production of styrene . Aluminophosphates (ALPO), generally have neutral framework and large pore sizes, like in VPI‐5.…”

Conversion of MeOH and Toluene into Styrene and Ethylbenzene Using Composite Catalysts Containing MeOH Dehydrogenation Components

“…Styrene is a key building‐block chemical for the production of polymers with significant application value . Producing styrene by side‐chain alkylation of toluene with methanol was deemed as a sustainable one‐step alternative to the present two‐step route via the alkylation of benzene with ethylene and sequential hydrogenation of the ethylbenzene product …”

“…It has been most frequently studied as a base catalyst and various modifications were made to improve its activity and selectivity for styrene . Up to now, the modification of CsX has been mainly concentrated on introducing boron containing compounds and alkali metal oxides ,,…”

Explaining the influence of the introduced base sites into alkali oxide modified CsX towards side-chain alkylation of toluene with methanol

“…1 Since then, this reaction has attracted widespread attention and was deemed as a sustainable one-step alternative for the current two-step route through the alkylation of benzene with ethylene and sequential dehydrogenation of the ethylbenzene product. 2,3 In spite of many studies in the past decades, there are still lots of unsolved problems, among which the relatively low catalytic conversion of reactants is the most urgent one as it is the main restriction for realizing industrial application of this potential and sustainable technology.…”

“…[10][11][12] According to a current consensus, cesium ion exchanged zeolite X (CsX) is the most promising catalyst for side-chain alkylation of toluene with methanol. 2,4,13 It was found that further modifying CsX with cesium oxide can greatly improve its catalytic activity for side-chain alkylation of toluene with methanol. 5,8,14,15 Archier et al found that modifying CsX with cesium oxides can promote the side-chain alkylation of toluene with methanol, and suggested it was attributed to the promotion for the generation of formaldehyde from methanol on the alkali oxides particles.…”