Catalytic Activity of Ni Based Materials Prepared by Different Methods for Hydrogen Production via the Water Gas Shift Reaction

Abstract

Water gas shift reactions (WGS) were evaluated over Ni/CeO2 and Ni/CeSmO catalysts for hydrogen production. The effects of catalyst preparation method and Sm loading were investigated. The Ni/ceria and Ni/CeSmO catalysts were synthesized by combustion, sol gel and sol gel-combustion method. After WGS tests, the catalysts were determined the carbon deposition by thermogravimetric analysis. The thermogravimetric analysis and temperature programmed NH3 desorption showed that addition of Sm promoter made higher the weak acid sites and lower the amount of carbon deposition than the unpromoted catalyst due to it being easily removed. CO chemisorption result indicated that Ni/Ce5%SmO catalyst prepared by combustion method has the highest Ni metal dispersion and metallic surface area compared to the other catalysts. The enhancement of WGS activity of this catalyst is due to more surface active sites being exposed to reactants. Furthermore, H2-temperature programmed reduction analysis confirmed an easiest reduction of this catalyst. This behavior accelerates the redox process at the ceria surface and enhances the oxygen vacancy concentration. The catalytic activity measurements exhibited that the optimum Sm loading was 5% wt. and the best catalyst preparation was the combustion method. The high surface area and small crystallite size of the 5%Ni/Ce5%SmO (combustion) catalyst resulted in sufficient dispersion, which closely related to the WGS activity of the catalyst.

Water–Gas Shift Activity over Ni/Al2O3 Composites

“…Among all the catalysts, 10%Ni/Al 2 O 3 exhibits the greatest BET surface area (98 m 2 /g) and nickel dispersion (6.74%). Generally, the high dispersion of Ni on the catalyst surface results in an increase in CO adsorption and facilitation of the redox cycle [13,14]. The average particle size of Ni was determined by H 2 chemisorption.…”

“…An enhancement of the acidity can increase CO adsorption on the catalyst surface because a CO reactant in the WGS reaction is a weak base. Furthermore, the surface acidity of the catalyst was proved to be beneficial for CO 2 desorption, leaving behind free active sites for CO and H 2 O adsorption in subsequent reaction cycles [13,14]. The total acidity can be calculated by integrating the NH 3 -TPD curves.…”

Monometallic and Bimetallic Catalysts Supported on Praseodymium-Doped Ceria for the Water–Gas Shift Reaction

“…[54]. When attention is drawn to the variation in Sm amount [12], it appears that the Ni catalyst with 5%Sm-doped CeO 2 gives the highest water-gas shift activity. The enhancement of Sm content to 15 wt.% leads to a lowering of nickel dispersion.…”

“…Thus, many efforts have been dedicated to improving the reducibility and catalytic performance of CeO 2 by doping it with other cations to generate more oxygen vacancies and develop its resistance to thermal sintering [8,9]. In this part, doping CeO 2 with aliovalent (such as Eu 3+ , La 3+ , Gd 3+ , and Sm 3+ ) cations [10][11][12] or isovalent (such as Zr 4+ , Hf 4+ , and Ti 4+ ) cations [13,14] has been well described in the literature. The incorporation of an aliovalent cation into the CeO 2 lattice produces oxygen vacancies by charge compensation on the final oxide materials [15].…”

Effect of Re Addition on the Water–Gas Shift Activity of Ni Catalyst Supported by Mixed Oxide Materials for H2 Production

“…Moreover, under calcination temperature, M should take the higher oxidation state, M 3+ (M = Sm and Gd). It can be concluded that Sm 3+ or Gd 3+ incorporation in the ceria lattice generates unbalanced charges and strain; thus, oxygen vacancy is expected to be generated [18][19][20].…”