19 research outputs found
Impact of Catalyst Geometry on Diffusion and Selective Catalytic Reduction Kinetics under Elevated Pressures
Numerical Modeling of Hydroperoxyl-Mediated Oxidative Dehydrogenation of Formic Acid under SCR-Relevant Conditions
Operando XAS study of the influence of CO and NO on methane oxidation by Pd/Al2O3
Methane oxidation on Pd/Al2O3 has been investigated using operando X-ray absorption spectroscopy (XAS) at the Pd K-edge. The influence of CO and NO on methane abatement has been addressed performing temperature programmed reaction runs while recording simultaneously XANES spectra. During CO oxidation Pd is reduced while methane conversion is shifted to higher temperature. NO strongly inhibits both CO and CH4 oxidation, despite the higher fraction of oxidized palladium
Operando high energy XRD study of Cu/La0.5Sr0.5CoO3 three-way catalyst under oscillating feed
Stable complete methane oxidation over palladium based zeolite catalysts
Increasing the use of natural gas engines is an important step to reduce the carbon footprint of mobility and power generation sectors. To avoid emissions of unburnt methane and the associated severe greenhouse effect of lean-burn engines, the stability of methane oxidation catalysts against steam-induced sintering at low temperatures (<500 °C) needs to be improved. Here we demonstrate how the combination of catalyst development and improved process control yields a highly efficient solution for complete methane oxidation. We design a material based on palladium and hierarchical zeolite with fully sodium-exchanged acid sites, which improves the support stability and prevents steam-induced palladium sintering under reaction conditions by confining the metal within the zeolite. Repeated short reducing pulses enable the use of a highly active transient state of the catalyst, which in combination with its high stability provides excellent performance without deactivation for over 90 h in the presence of steam.ISSN:2041-172
Interconversion between Lewis and Brønsted-Lowry acid sites on vanadia-based catalysts
Lewis acid sites (LAS) and Brønsted-Lowry acid sites (BAS) play key roles in many catalytic processes, particularly in the selective catalytic reduction (SCR) of nitrogen oxides with ammonia. Here we show that temperature, gas feed, and catalyst composition affect the interplay between LAS and BAS on vanadia-based materials under SCR-relevant conditions. While different LAS typically manifest as a single collective peak in the steady-state spectra, their individual signals could be isolated through the increased sensitivity of transient experimentation. Furthermore, water could increase BAS not just by converting pre-existing LAS, but also by generating spontaneously new acid sites. These results pave the way for understanding the relationship between LAS and BAS, and how their ratio determines the reactivity of vanadia-based catalysts not just in SCR but in other chemical transformations as well