Search

• The influences of electronic metal-support interactions (EMSI) on the catalytic hydrogenation of ethylene over Pd n /CeO2 (n = 4, 7, 10) have been studied. • The charge redistribution on the Pd cluster creates 2 typical sites: IF sites located at the interface between metal and support and T sites located at the topmost of the cluster. • IF sites show extremely higher activity for H 2 dissociation and T sites show better activity for ethylene hydrogenation. • At high H coverage, both the kinetics and thermodynamics of the hydrogenation reaction would be significantly promoted. • The two types of sites should collaborate synergically to promote the hydrogenation process. The catalytic activity of supported catalyst is closely related to the electronic metal-support interactions (EMSI). In this paper, first principles density functional theory study was conducted to understand the EMSI between Pd clusters (Pd 4 , Pd 7 , Pd 10) and CeO 2 substrate. When Pd was loaded on CeO 2 surface, the electrons of Pd would transfer to the CeO 2 substrate via Pd-O bonding interactions. Moreover, the charge redistribution on the Pd cluster leads to significant polarization of electron density. Consequently, the Pd atoms located at the metal-support interface (IF site) are positively charged, while the Pd atoms at the topmost (T site) are negatively charged. The H 2 dissociation and ethylene hydrogenation at these sites were calculated with both low and high hydrogen coverage. It was found that the two types of sites should collaborate synergically to promote the hydrogenation of ethylene. In particular, the IF sites exhibit relatively high activity for H 2 dissociation, while the T sites show superior catalytic efficiency for ethylene hydrogenation. Therefore, the EMSI induced charge polarization can tune the electronic structure and charge state of supported metal catalysts, which further determines the performance of different region on the catalyst. [Display omitted] [ABSTRACT FROM AUTHOR]

• The mechanism of selective catalytic reduction (SCR) on spinel TiMn 2 O 4 (001) surface has been studied via DFT simulations. • The water molecules could serve as a hydrogen exchanger and play a positive role in promoting the SCR process. • The overall SCR process is highly exothermic with modest activation barriers on TiMn 2 O 4 (001) surface. • The spinel TiMn 2 O 4 is a promising catalyst for low temperature SCR. Manganese based spinel oxides is one of the most promising catalysts for low temperature selective catalytic reduction (SCR) process due to its high activity and tunable composition. Understanding the molecular-level reaction mechanism of SCR on Mn-containing spinel oxides is of great importance for design and development of appropriate catalyst for low temperature SCR process. In this paper, density functional theory calculations were performed to address the detail SCR reaction pathways between NH 3 and NO on spinel TiMn 2 O 4 (001) surface. The full SCR process was found to be divided into four sequential stages, including the NH 3 chemisorption (stage i), NH 2 NO formation (stage ii), H migration (stage iii), and products desorption (stage iv). Notably, we found that water molecules could serve as a hydrogen exchanger and play a positive role in promoting the hydrogen migration during stage i and stage iii of the SCR process. Thermodynamically, the overall SCR process is highly exothermic with the reaction energy of -3.054 eV. Kinetically, the formation of NH 2 NO intermediate was identified as the rate determining step with a moderate activation barrier of 1.064 eV. Our results suggest that the spinel TiMn 2 O 4 is a promising catalyst for low temperature SCR. Moreover, the promoting effect of water on hydrogen diffusion should be also applicable to other chemical reactions involving hydrogen transfer. [Display omitted] [ABSTRACT FROM AUTHOR]