Oxidative Reforming of Methane over Rh-Containing Zeolites: Active Species and Role of Zeolite Framework

Abstract

Rh ion-exchanged Y zeolite (Rh-Y) and amorphous silica−alumina (Rh-ASA) were prepared by the ion-exchange method. The Rh species were identified by UV−vis and IR spectroscopies, TEM, and H 2 -TPR measurements. Isolated Rh cations were preferentially formed on the Y zeolite, while Rh oxide mainly existed on ASA. The catalytic activities of the prepared samples for oxidative reforming of methane were evaluated. The Rh oxide on Rh-ASA exhibited slightly higher methane conversion and CO yield than those of the isolated Rh cation on Rh-Y. On the other hand, the catalytic lifetime over Rh-Y was longer than that over Rh-ASA because the isolated Rh cations were protected from aggregation by electrostatic interaction with the zeolite framework. In addition, Rh-Y exhibited a high catalytic activity even at low Rh contents owing to its high dispersibility. On the basis of the experimental facts, we have successfully clarified the active Rh species for this oxidative reforming of methane and demonstrated the effectiveness of the zeolite framework for the stabilization of the active species. This article provides the important concept for the design of highly active catalysts in this catalytic system.

Active site for syngas production by direct partial oxidation of CH4 over ZrO2

“…Supported Ni and Rh catalysts enable direct POM. 7,18–22 The formation of syngas in the presence of O 2 confirms that the POM reaction proceeds via the direct route. 7,23–25 Syngas formation has been seen in the presence of O 2 using supported Rh catalysts.…”

Zeolite-based catalysts for oxidative upgrading of methane: design and control of active sites

“…Furthermore, we investigated the role of the zeolite framework in this reaction by using model catalysts. 73 To this…”

“…Furthermore, we investigated the role of the zeolite framework in this reaction by using model catalysts. 73 To this end, we prepared two kinds of model catalysts: Rh ion-exchanged Y zeolite (Rh-Y) and amorphous silica-alumina (Rh-ASA). The Rh species were characterized by UV-vis and in situ FT-IR spectroscopies, transmission electron microscopy (TEM), and H 2 temperature-programmed reduction (H 2 -TPR) measurements.…”

Improvement of Catalytic Activity of Ce-MFI-Supported Pd Catalysts for Low-Temperature Methane Oxidation by Creation of Concerted Active Sites

“…Methane is the simplest and most abundant alkane, and the development of efficient upgrading processes for methane to produce chemical feedstocks has long been desired. − In addition, the demand for such technology has been increasing since the shale gas revolution in the United States in 2006 . However, relatively severe reaction conditions are required for the activation of methane because of the high dissociation energy of C–H bonds (∼440 kJ mol –1 ). , The reforming of methane, including steam, dry, and oxidative reforming reactions, ,,− is one of the key processes for producing syngas (a mixture of CO and H 2 ), which can be subsequently transformed into valuable hydrocarbons via the Fischer–Tropsch process. − However, these reactions have some disadvantages: (1) The product yields are constrained by the thermodynamic equilibrium in most cases. ,,− (2) This multistep reaction requires a high energy input to obtain hydrocarbons …”