Thermal Alteration in Adsorption Sites over SAPO‐34 Zeolite

Abstract

Zeolites have found tremendous applications in the chemical industry. However, the dynamic nature of their active sites under the flow of adsorbate molecules for adsorption and catalysis is unclear, especially in operando conditions, which could be different from the as‐synthesized structures. In the present study, we report a structural transformation of the adsorptive active sites in SAPO‐34 zeolite by using acetone as a probe molecule under various temperatures. The combination of solid‐state nuclear magnetic resonance, in situ variable‐temperature synchrotron X‐ray diffraction, and in situ diffuse‐reflectance infrared Fourier‐transform spectroscopy allow a clear identification and quantification that the chemisorption of acetone can convert the classical Brønsted acid site adsorption mode to an induced Frustrated Lewis Pairs adsorption mode at increasing temperatures. Such facile conversion is also supported by the calculations of ab‐initio molecular‐dynamics simulations. This work sheds new light on the importance of the dynamic structural alteration of active sites in zeolites with adsorbates at elevated temperatures.

Development and study of a bifunctional photocatalyst based on SAPO-34 molecular sieve

“…The mechanism of the composite molecular sieve photocatalyst for the degradation of formaldehyde was investigated based on the energy band structure of BiVO 4 with the HOMO and LUMO energy levels of SAPO-34, and by free radical burst experiments. The bridge formed by the O element could transfer the electrons generated by the BiVO 4 crystal into the LUMO energy level of the SAPO-34 molecular sieve, 14 inhibiting the rate of electron–hole combination in the BiVO 4 crystal. The active sites of B-acids and L-acids in the molecular sieve were enriched, while the LUMO energy level attracted a large number of electrons to occupy its own holes, which made a large number of electrons in the HOMO energy level participate in the process of degrading formaldehyde and hence accelerated the degradation rate of formaldehyde.…”

“…Both of these methods affect the distribution of active sites within the molecular sieve, 13 while the aggregation of semiconductors creates a significant impediment to the movement of molecules within the pores. 14 Therefore, increasing the mass transfer rate of reactants and products and enriching the active sites within the molecular sieve have become pressing issues. 15,16 One potential strategy to solve these problems is to introduce a semiconductor catalyst in the form of ions into the pores of the molecular sieve subsequently forming a semiconductor catalyst within the pores of the molecular sieve by hydrothermal means, solving the problem of an uneven dispersion of the semiconductor catalyst within the molecular sieve.…”

Semi-quantitative determination of active sites in heterogeneous catalysts for photo/electrocatalysis

“…102 Similar active site transformations can also be promoted at elevated temperatures. 103 These ndings highlight the importance of using combined characterizations and in situ techniques for active site identication.…”

Understanding the Facile Heterolytic Dissociation of Hydrogen on Natural Surface Frustrated Lewis Pairs

“…Until now, solid FLPs catalysts have been designed and constructed based on a variety of solid materials, including modified metal oxides such as In 2 O 3– x (OH) y , defect CeO 2 and TiO 2 , − two-dimensional materials, − metal–organic frameworks (MOFs), − and zeolites. − One of the earliest examples is the finding of surface FLPs on In 2 O 3– x (OH) y , where the In···OH Lewis pair satisfies the concept of FLPs and is responsible for the heterolytic dissociation of H 2 . Another simple and effective strategy to construct surface FLPs is creating oxygen vacancies on metal oxide surfaces, where the exposed metal cations and their second neighboring oxygen form M···O FLPs.…”