Surface properties of Ca, Ti‐doped CeO₂ and their influence on the reverse water‐gas shift reaction

Abstract

CeO2‐based materials can be found in a variety of catalytic processes, including the reverse water‐gas shift (RWGS) reaction. Nevertheless, the interaction of molecular gases with the surfaces of such materials is still not clear. Recently, some progress was reported on the incorporation of neodymium (Nd) and calcium (Ca) into ceria and their effect on H2O and CO2 adsorption. Titanium (Ti), which has a much smaller ionic radius, has the ability to change the interaction landscape, both as a co‐dopant to Ca and as a sole dopant in the CeO2 system. In this study, the interactions of environmental gases (i.e., water vapor and CO2) on the surface of Ti‐doped CeO2 and Ca,Ti co‐doped CeO2 were investigated. Ti addition to CeO2 was shown to decrease water vapor uptake by up to 25% all while maintaining similar heats of adsorption. In the case of CO2 adsorption, Ti addition to CeO2 had lowered the uptake by more than 50% as well as lowering the heat of adsorption. Co‐doping with Ti and Ca showed small decrease in H2O uptake accompanied with increased heat of adsorption. For CO2, the changes to the uptake and energetics were small and did not indicate a specific trend. The RWGS catalytic performance showed improvement by the addition of Ti in certain levels. The relationship between the doping, surface properties, gas‐surface interactions, and catalytic performance is discussed.

Two decades of ceria nanoparticle research: structure, properties and emerging applications

“…Doping CeNPs with transition metals or rare earth metal such as Cu, Cr, Ti, Y, and La have been adopted as a promising approach to tune the catalytic activity of these materials. [326][327][328][329][330] The substitution process causes structural defects and creates more oxygen vacancies on the catalyst surface, which affects the generation and mobility of charged species such as electrons and oxygen anions. Furthermore, doped ceria can also tolerate high temperature annealing treatments due to the cooperative nature of the cations of the binary oxides.…”

Enhanced Oxygen Storage Capacity of Porous CeO2 by Rare Earth Doping

“…Even after the loss of oxygen from the lattice and the consequent formation of numerous V O , CeO 2− x still retains a fluorite crystal structure [ 19 , 20 ] and captures oxygen by filling the V O upon exposure to oxygen, accompanied by the recovery of CeO 2 [ 21 ]. Moreover, the doping of other metallic elements into the CeO 2 lattice could control their structure and physical properties [ 22 , 23 , 24 ], such as rare–earth elements [ 25 , 26 , 27 ], transition elements [ 28 , 29 , 30 ] and alkaline earth elements [ 31 , 32 , 33 ]. In spite of the successful synthesis of CeO 2 –based composite oxides, most of the previous reports have focused on the investigation of catalytic performances [ 34 , 35 ], transport properties [ 36 , 37 ] and the origin of room–temperature ferromagnetism [ 38 , 39 ], the theoretical data about OSC were usually quite scattered, and only a few fundamental studies on the OSC of doped CeO 2 have been reported.…”