(512c) Study of Catalytic NO+CO and Dry Reforming Reaction over CoOx/CeO2: Molecular and Electronic Structure-Activity Relationships

Anthropogenic greenhouse gas emissions into the atmosphere are a growing global warming concern. Over the last several decades, valorization of greenhouse gases (e.g., CO, CO2, NOx, and CH4) and transformation of natural gas to syngas (H2+CO) has been extensively investigated. Nitrogen oxides (NOx) are a main contributor—in addition to HC, COx, SOx, and PM—to global air pollution. In the last several decades, platinum group metals (PGMs) and zeolites have been extensively applied to NOx abatement. Although these catalysts exhibit a high level of catalytic activity, NOx decomposition over PGMs and zeolites has some practical issues such as high cost and high light-off temperature. To resolve these issues, transition metal oxide catalysts have been investigated for low temperature NOx decomposition reaction by CO with varied O2 concentrations, which is a primary reaction in three-way catalysis (TWC). Dry reforming of methane (DRM) utilizes CH4 and CO2 mixture for syngas production: CH4+CO2 = 2H2+2CO. From a fundamental perspective, in the DRM process, CO2 offers a poor source of O to the C-H bond activation process, on account of large activation barriers to extract O from this molecule unlike the case of O2 and H2O. As a result, the DRM reaction involves a soft oxidative activation during the conversion of CH4. Since the interaction with CH4 and CO2 can change the chemical state of a catalyst, a detailed study of the DRM process using in-situ techniques can lead to a fundamental knowledge on how to activate CH4 selectively by avoiding pathways to complete oxidation, hence benchmarking catalyst behavior under difficult reaction conditions.

In the current talk, I will describe the relationship between molecular /electronic structure and catalytic activity for the NO+CO and the DRM reaction over a series of ceria-supported cobalt catalysts. We will present the structural, morphological and chemical properties of the synthesized catalysts examined by several characterization techniques under ex-situ and in-situ conditions. Our studies show a dynamical evolution in the chemical composition of the catalysts under reaction conditions. In-situ results indicate that under reaction conditions, the active state (e.g., metallic Co and Co3+/4+) of the catalyst is changed under different reaction conditions.