Activation of CO and NO Over MnOx/TiO2 Surfaces: Mechanistic Investigations

University Of Cincinnati Main Campus, Cincinnati OH

Investigators

Abstract

CBET-0828226 Smirniotis This proposal describes research plans for the fundamental understanding of CO activation over the surface of MnOx/TiO2 in the presence of another chemical species and excess oxygen. This study focuses on specific cases of reactions where in CO is not oxidized to CO2 (non-selective) but it is rather utilized towards a selective chemical transformation. This work is inspired by our remarkable findings of using CO as a reductant for the transformation of NO into di-nitrogen. More specifically, we found that the MnOx/TiO2 catalyst is highly active for the reduction of NO with CO, giving more than 90% NO conversion at 200 °C at very high space velocity (GHSV = 50,000 h-1). The activity of the reaction increased in presence of oxygen and the reaction is highly selective in the presence of oxygen. Our in-situ FT-IR studies revealed that the reaction mechanism on MnOx/TiO2 is different from that reported earlier over supported metal and perovskites-based catalysts, on account of the non-formation of -NCO species, which is widely reported as intermediate. The non-formation of -NCO species was confirmed by the absence of prominent absorbance band at 2178 cm-1. A balanced program for the synthesis, characterization with modern techniques, and kinetic studies to reveal the reaction pathways/mechanism over the proposed catalysts will be performed. It is expected that the proposed research will provide a fundamental understanding of the surface chemistry and reaction pathways occurring during the activation of CO in the presence of NO over Mn/TiO2 catalysts in the range of 150 to 350 °C in the presence of high concentrations of oxygen. Our studies will focus on reactions of CO with NO, where the latter compounds serve as a promoter for the selective transformations observed. The specific role of Mn leading to the increased selectivity and activity observed at low temperatures, and high tolerance to water will be investigated thoroughly. Extensive surface characterizations, kinetic and isotopic labeling studies experiments will be carried to explain the remarkable selectivity observed. Moreover, these tools will be used to obtain useful insights for the role of Mn in activating CO and NO, understand the nature of the intermediate surface species, and will identify the role of surface species on the reaction mechanism. The proposed research has unique practical implications in relation to environment and energy which are areas of great importance for the future. The proposed work is expected to broadly impact the scientific knowledge base, education, and society in general. The overriding drivers are both the formulation of more effective environmental processes, and developing new technological concepts that advance the current state-of-the-art in catalysis using CO. The impact on education is expected to be manifold. Through the development of innovative hands-on demonstrations for high school students, poster presentations and showcase participation at the community level, and multidisciplinary seminars to industry and academia, a broad constituency will be introduced to the field. Undergraduate students will be involved in the research, to encourage innovation and spark an interest in graduate education. A particular emphasis will be placed on recruiting under-represented minorities and women. The proposed work has potentially high socioeconomic impact. If funded it will provide advanced catalysts more economic to operate for air pollution control. Moreover, the knowledge gained on selectively transforming CO, will be extended to other important environmental and energy related processes.