ChemInform Abstract: NMR and IR Studies of Zeolite H‐ZSM‐5 Modified with Orthophosphoric Acid.

Abstract

009ChemInform Abstract The results of 1H NMR self-diffusion experiments show that H3PO4 penetrates into the channel network of the ZSM-5 zeolite. At higher H3PO4 concentrations, an enrichment of phosphorus deposits near the external surface is observed. 27Al, 29Si, and 31P MAS NMR results show that dealumination and formation of polyphosphoric acids occurs during calcination of the H3PO4-modified zeolite. The decreased number of Broensted acid sites in the modified zeolite after heat treatment at 500 rc C is a direct result of the framework dealumination. A study of the influence of H3PO4 impregnation of H-ZSM-5 on the selective toluene disproportionation reveals a higher paraselectivity and lower catalytic activity of the modified zeolites.

Solid-state MAS NMR studies on the hydrothermal stability of the zeolite catalysts for residual oil selective catalytic cracking

“…As a result of orthophosphoric acid impregnation, the intensity of the Brønsted acid decreased (Figs. 2c and d), which can be explained exclusively by a framework dealumination [30], which is in good agreement with the results of 29 Si MAS NMR spectra. It should be noted that POH from orthophosphoric acid can also contribute to the signal centered at 2.2 ppm in the 1 H MAS NMR spectra.…”

Local silico-aluminophosphate interfaces within phosphated H-ZSM-5 zeolites

“…42 The signal at À12 ppm is often attributed to middle chain phosphate groups. 42 The strongest Al-P interactions through space are found for the À15 ppm signal. Resonance 5 interacts with a variety of 31 P resonances.…”

“…Not surprisingly, many models for possible interactions have been discussed over the years, where the main division of opinion lies between the question whether permanent phosphorus-framework interaction exists or not. 14,17,19,[26][27][28][29][30]42 In the case of permanent phosphorus-framework interaction the most intuitive explanation would be the incorporation of phosphorus into the zeolitic framework. However, the Si-O-P bonds that are required for such a substitution have never been found in either phosphorus/H-ZSM-5 or SAPO materials and theoretical work has pointed to the unlikeliness of such bonds.…”

“…14 Caro and co-workers also proposed that phosphorus only interacted with extra-framework aluminium and that dealumination leads to a decrease in acid sites. 42 These disagreements on zeolite-phosphorus interaction have led to much confusion with regard to the interpretation of data and spectra, as different authors attribute similar peaks to different species, e.g. in 27 Al MAS NMR and especially 31 P MAS NMR.…”

“…in 27 Al MAS NMR and especially 31 P MAS NMR. 14,17,18,42 Another complicating factor is the synthesis conditions used during phosphatation, which vary for different studies. There are three parameters that can affect the structure of the zeolite material, namely (i) acidity coming from the acidic precursor H 3 PO 4 , which is often used, (ii) thermal treatment that is customarily performed after phosphorus introduction, and (iii) the actual presence of phosphorus species.…”