1
|
Jain SK, Tabassum T, Li L, Ren L, Fan W, Tsapatsis M, Caratzoulas S, Han S, Scott SL. P-Site Structural Diversity and Evolution in a Zeosil Catalyst. J Am Chem Soc 2021; 143:1968-1983. [PMID: 33491456 DOI: 10.1021/jacs.0c11768] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Phosphorus-modified siliceous zeolites, or P-zeosils, catalyze the selective dehydration of biomass derivatives to platform chemicals such as p-xylene and 1,3-butadiene. Water generated during these reactions is a critical factor in catalytic activity, but the effects of hydrolysis on the structure, acidity, and distribution of the active sites are largely unknown. In this study, the P-sites in an all-silica self-pillared pentasil (P-SPP) with a low P-loading (Si/P = 27) were identified by solid-state 31P NMR using frequency-selective detection. This technique resolves overlapping signals for P-sites that are covalently bound to the solid phase, as well as oligomers confined in the zeolite but not attached to the zeolite. Dynamic Nuclear Polarization provides the sensitivity necessary to conduct 29Si-filtered 31P detection and 31P-31P correlation experiments. The aforementioned techniques allow us to distinguish sites with P-O-Si linkages from those with P-O-P linkages. The spectra reveal a previously unappreciated diversity of P-sites, including evidence for surface-bound oligomers. In the dry P-zeosil, essentially all P-sites are anchored to the solid phase, including mononuclear sites and dinuclear sites containing the [Si-O-P-O-P-O-Si] motif. The fully-condensed sites evolve rapidly when exposed to humidity, even at room temperature. Partially hydrolyzed species have a wide range of acidities, inferred from their calculated LUMO energies. Initial cleavage of some P-O-Si linkages results in an evolving mixture of surface-bound mono- and oligonuclear P-sites with increased acidity. Subsequent P-O-P cleavage leads to a decrease in acidity as the P-sites are eventually converted to H3PO4. The ability to identify acidic sites in P-zeosils and to describe their structure and stability will play an important role in controlling the activity of microporous catalysts by regulating their water content.
Collapse
Affiliation(s)
- Sheetal K Jain
- Department of Chemistry & Biochemistry, University of California, Santa Barbara, California 93106, United States
| | - Tarnuma Tabassum
- Department of Chemistry & Biochemistry, University of California, Santa Barbara, California 93106, United States
| | - Li Li
- Department of Chemistry & Biochemistry, University of California, Santa Barbara, California 93106, United States
| | - Limin Ren
- Department of Chemical Engineering and Materials Science, University of Minnesota, 421 Washington Ave SE, Minneapolis, Minnesota 55455, United States
| | - Wei Fan
- Department of Chemical Engineering, University of Massachusetts Amherst, 686 North Pleasant Street, Amherst, Massachusetts 01003, United States
| | - Michael Tsapatsis
- Department of Chemical and Biomolecular Engineering and Institute for NanoBiotechnology, Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218, United States.,Applied Physics Laboratory, Johns Hopkins University, 11100 Johns Hopkins Road, Laurel, Maryland 20723, United States
| | - Stavros Caratzoulas
- Delaware Energy Institute, 221 Academy Street, Newark, Delaware 19716, United States
| | - Songi Han
- Department of Chemistry & Biochemistry, University of California, Santa Barbara, California 93106, United States.,Department of Chemical Engineering, University of California, Santa Barbara, California 93106, United States
| | - Susannah L Scott
- Department of Chemistry & Biochemistry, University of California, Santa Barbara, California 93106, United States.,Department of Chemical Engineering, University of California, Santa Barbara, California 93106, United States
| |
Collapse
|
2
|
van der Bij HE, Weckhuysen BM. Phosphorus promotion and poisoning in zeolite-based materials: synthesis, characterisation and catalysis. Chem Soc Rev 2015; 44:7406-28. [PMID: 26051875 PMCID: PMC4672753 DOI: 10.1039/c5cs00109a] [Citation(s) in RCA: 117] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Complex interactions between phosphorus and zeolites are related to several promotional and poisoning effects in zeolite catalysis.
Phosphorus and microporous aluminosilicates, better known as zeolites, have a unique but poorly understood relationship. For example, phosphatation of the industrially important zeolite H-ZSM-5 is a well-known, relatively inexpensive and seemingly straightforward post-synthetic modification applied by the chemical industry not only to alter its hydrothermal stability and acidity, but also to increase its selectivity towards light olefins in hydrocarbon catalysis. On the other hand, phosphorus poisoning of zeolite-based catalysts, which are used for removing nitrogen oxides from exhaust fuels, poses a problem for their use in diesel engine catalysts. Despite the wide impact of phosphorus–zeolite chemistry, the exact physicochemical processes that take place require a more profound understanding. This review article provides the reader with a comprehensive and state-of-the-art overview of the academic literature, from the first reports in the late 1970s until the most recent studies. In the first part an in-depth analysis is undertaken, which will reveal universal physicochemical and structural effects of phosphorus–zeolite chemistry on the framework structure, accessibility, and strength of acid sites. The second part discusses the hydrothermal stability of zeolites and clarifies the promotional role that phosphorus plays. The third part of the review paper links the structural and physicochemical effects of phosphorus on zeolite materials with their catalytic performance in a variety of catalytic processes, including alkylation of aromatics, catalytic cracking, methanol-to-hydrocarbon processing, dehydration of bioalcohol, and ammonia selective catalytic reduction (SCR) of NOx. Based on these insights, we discuss potential applications and important directions for further research.
Collapse
Affiliation(s)
- Hendrik E van der Bij
- Inorganic Chemistry and Catalysis, Debye Institute for Nanomaterials Science, Faculty of Science, Utrecht University, Universiteitsweg 99, 3584 CG, Utrecht, The Netherlands.
| | | |
Collapse
|