Unique properties of silver cations in solid-acid catalysis by zeolites and heteropolyacids

文献情報

出版日 2015-05-19

DOI 10.1039/C5CP01839K

インパクトファクター 3.676

著者

Yoshio Ono, Toshihide Baba

原文を見る

要旨

Ag+-exchanged zeolites exhibit unique catalytic properties caused by the combination of their redox and acidic properties. Partial reduction of Ag+ ions in zeolites with hydrogen leads to the formation of acidic protons and silver metal particles, which can be observed using X-ray powder diffraction patterns (XRD). By simply evacuating hydrogen from the system, the silver metal particles are returned back to Ag+ ions and at the same time, acidic protons are eliminated. This interconversion of Ag+ ions and silver metal or gaseous hydrogen and surface protons is reflexed in the catalytic activities of Ag+-exchanged zeolites for acid-catalyzed reactions: the activity of Ag+-exchanged Y zeolite (Ag-Y) reversibly changes with the partial pressure of hydrogen. Furthermore, the activity of Ag-Y in the presence of hydrogen is higher than that of H+-exchanged Y zeolite (H-Y). Similar phenomena are also observed for the silver salt of dodecatungstophosphoric acid (Ag3PW12O40). Ag+-exchanged ZSM-5 zeolite (Ag-ZSM-5) is a very selective catalyst for aromatization of alkanes, alkenes and methanol. Examination of the activation step of lower alkanes revealed that Ag+ ions dramatically enhance the dehydrogenation of the alkanes via heterolytic dissociation of the alkanes into carbenium ions and hydride species. Ag+-exchanged zeolites can also activate methane. The reaction of methane with ethene and benzene gives propene and toluene, respectively. Ag-ZSM-5 is a very stable catalyst under hydrothermal conditions because of the interconversion properties of Ag+ ions and silver metal in the zeolite.

掲載誌

Physical Chemistry Chemical Physics

CiteScore: 5.5

自己引用率: 10.3%

年間論文数: 3036

Physical Chemistry Chemical Physics (PCCP) is an international journal co-owned by 19 physical chemistry and physics societies from around the world. This journal publishes original, cutting-edge research in physical chemistry, chemical physics and biophysical chemistry. To be suitable for publication in PCCP, articles must include significant innovation and/or insight into physical chemistry; this is the most important criterion that reviewers and Editors will judge against when evaluating submissions. The journal has a broad scope and welcomes contributions spanning experiment, theory, computation and data science. Topical coverage includes spectroscopy, dynamics, kinetics, statistical mechanics, thermodynamics, electrochemistry, catalysis, surface science, quantum mechanics, quantum computing and machine learning. Interdisciplinary research areas such as polymers and soft matter, materials, nanoscience, energy, surfaces/interfaces, and biophysical chemistry are welcomed if they demonstrate significant innovation and/or insight into physical chemistry. Joined experimental/theoretical studies are particularly appreciated when complementary and based on up-to-date approaches.