Chaoquan Hu

NiCo2O4 3 dimensional nanosheet as effective and robust catalyst for oxygen evolution reaction

Water electrolysis plays a fundamental role in the development of a sustainable energy system. In practice the efficiency of water electrolysis is severely limited by the sluggish kinetics of the oxygen evolution reaction. We reported a kind of integrated 3 dimensional oxygen evolution reactions (OER) catalyst by growing NiCo2O4 nanosheet arrays directly on conductive substrates. Such self-supported NiCo2O4 nanosheet electrodes exhibit high catalytic activity, good durability and nearly 100% faradic efficiency (FE) in alkaline electrolyte due to the enlarged electrochemical surface area and reduced electron transference resistance.

High-quality hydrogen generated from formic acid triggered by in situ prepared Pd/C catalyst for fuel cells

High-quality hydrogen can be generated from formic acid triggered by facilely in situ prepared Pd/C catalyst in ambient conditions. The obtained gas can be directly fed into proton exchange membrane fuel cells indicating a very promising application.

Selectivity and kinetics of methyl crotonate hydrogenation over Pt/Al2O3

The hydrogenation of gas-phase methyl crotonate (MC) over Pt/Al2O3 was investigated with the aim to understand CC hydrogenation in unsaturated methyl esters. Three Pt/Al2O3 catalysts with different Pt dispersions were prepared by varying calcination temperature and evaluated for MC hydrogenation. The main products were found to be methyl butyrate (MB) and methyl 3-butenoate (M3B), resulting from hydrogenation and shift of the CC bond in MC, respectively. The measured activity for both hydrogenation and shift of the CC in MC was found to depend on the Pt dispersion where higher Pt dispersion favors the CC hydrogenation reaction. The effect of reactant concentrations on the activity and selectivity for MC hydrogenation over the Pt/Al2O3 catalyst was examined in detail. Under the investigated conditions, the CC hydrogenation was found to have a negative reaction order with respect to MC concentration but a positive H2 order. Further understanding of the MC hydrogenation was provided from H2 chemisorption experiments over the catalyst with and without pre-adsorbed MC and from transient experiments using alternating MC and H2 feeds. Based on the present experimental results, a reaction pathway was proposed to describe gas-phase MC hydrogenation over Pt/Al2O3. In order to gain more insight into the reaction, a kinetic analysis of MC hydrogenation was performed by fitting a power-law model to the kinetic data, moreover, dissociative H2 adsorption on the catalyst was found to be the rate-determining step by comparing the power-law model with the overall rate expressions derived from mechanistic considerations.

Mechanistic insights into complete hydrogenation of 1,3-butadiene over Pt/SiO2: effect of Pt dispersion and kinetic analysis

Gas-phase hydrogenation of 1,3-butadiene was investigated over Pt/SiO2 catalysts with the aim of understanding the complete hydrogenation of dienes. The measurements focused on the effect of Pt dispersion on the product distribution and the kinetics of n-butane formation. Under the investigated conditions with an excess of hydrogen, the selectivity to n-butane sharply decreased from 41.6% to less than 3% at a 1,3-butadiene conversion of ∼10% when the average Pt particle size increased from 3.9 to 22 nm. Correspondingly, the apparent activation energy for n-butane formation was measured to increase by about 2.7 times. In situ diffuse reflectance infrared Fourier transform (DRIFT) observations via alternating 1,3-butadiene and hydrogen feeds over the catalysts demonstrated that 1-butene was the major reaction intermediate in the process of 1,3-butadiene hydrogenation. By analysis of the kinetic data using the Horiuti–Polanyi mechanism with 1-butene as the intermediate, different reactivities of hydrogen on the catalysts towards CC bond hydrogenation were proposed to understand the variation of the selectivity to n-butane with Pt dispersion. This viewpoint was further supported by DFT calculation of 1-butene hydrogenation with hydrogen at different sites on the Pt(111) surface.

Reaction pathway for partial hydrogenation of 1,3-butadiene over Pt/SiO2

The reaction pathway for partial hydrogenation of 1,3-butadiene over a Pt/SiO2 catalyst was explored with a combination of in situ diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, intrinsic kinetics, and density functional theory (DFT) calculations. Under the present experimental conditions, the catalyst displayed a nearly constant product composition with ∼97% selectivity to butenes. In situ DRIFT characterization revealed that the 1-buten-3-yl radical (1B3R), generated from the addition of one hydrogen atom to a terminal carbon of 1,3-butadiene, was the dominant intermediate in the partial hydrogenation of 1,3-butadiene. Kinetic analysis showed that the hydrogenation of 1B3R was the rate-determining step in the formation of butenes. Based on the above experimental results, DFT calculations were employed to investigate the reaction pathway with 1B3R as the intermediate on a Pt(111) surface. Interestingly, it was found that 1B3R can be easily formed from the hydrogenation of 1,3-butadiene with a di-σ configuration rather than the most stable tetra-σ structure on the Pt(111) surface. This hydrogenation step occurs between the non-coordinated terminal carbon and a hydrogen atom on a top site with an energy barrier of 23.2 kJ mol−1. The second hydrogenation step from 1B3R to butenes requires relatively higher activation barriers to proceed, being consistent with the experimental kinetics. Finally, the selectivity order for butenes and the structure sensitivity of Pt-catalyzed partial hydrogenation of 1,3-butadiene were discussed.