Size-Dependent Surface Basicity of Nano-CeO2 and Desorption Kinetics of CO2 on Its Surface

Effect of Support on Stability and Coke Resistance of Ni-Based Catalyst in Combined Steam and CO2 Reforming of CH4

Ni-based catalysts dispersed on different supports (MgO-α-Al₂O₃, CeO₂, SBA-15, and MgO-SBA-15) were prepared by the impregnation method. Characteristics of the catalysts, including specific surface areas (N₂ physisorption), crystalline phase compositions (powder X-ray diffraction, Raman spectroscopy), reducibility (hydrogen temperature-programmed reduction, H₂-TPR), and morphology (scanning electron microscopy (SEM) and transmission electron microscopy, TEM)) were investigated. The activity and stability of the catalysts were tested for the combined steam and CO₂ reforming of methane at 700 °C in a microflow system. The results show that the catalysts exhibit high activity in the BRM reaction. At 700 °C, the conversion of CH₄ and CO₂ reached 86-99% and 67-80%, respectively, in which the Ni/Mg-SBA catalyst is the best with conversions of CH₄ and CO₂ reaching 99% and 80%. Coke accumulation on the surface of the catalysts for 100 h time on stream (TOS) was evaluated by the temperature-programmed oxidation (TPO) technique. The major cause of the catalytic deactivation was elucidated by combining the determination of the amount and type of deposited coke with the changes in the physicochemical properties of the catalysts after the long-term reaction. Almost complete loss of activity was observed on Ni/Mg-Al catalyst after 100 h TOS, while the activity drop was slow on the Ni/Mg-SBA sample, about 15-20% of the total value. Otherwise, the Ni/CeO₂ and Ni/SBA catalysts firmly retained their stable activity for 100 h TOS due to the minimal carbon deposition and stability of these catalysts' structure. The highly considerable formation of inert C_γ carbon and sintering over Ni catalyst supported on MgO-α-Al₂O₃ were responsible for the lower stability of this catalyst compared to those supported on CeO₂ and SBA-15.

Surface basicity mediated rapid and selective adsorptive removal of Congo red over nanocrystalline mesoporous CeO2

Herein we first report surface basicity mediated rapid and selective adsorptive removal of organic pollutants over nanocrystalline mesoporous CeO₂. The role of surface features in controlling the selectivity and efficiency of adsorption is well known. Nevertheless, the possibility of tuning the adsorption capacity and selectivity of adsorbents through their surface characteristics remains less explored. In this work, the surface basicity of mesoporous CeO₂ nanoparticles was improved by Er³⁺ doping under two different reaction conditions: via sol-gel and sol-hydrothermal methods. The nature and amount of surface basic sites were determined with the help of CO₂ temperature programmed desorption (TPD). The adsorption capacity and selectivity of four different CeO₂ samples were investigated using Congo red, methyl orange, and methylene blue as the model pollutants. From the adsorption studies, Er³⁺ doped CeO₂ synthesized by the sol-gel method, having the highest amount of surface basic sites, proved to be the most efficient and highly selective adsorbent among the four developed variants of CeO₂ towards Congo red. According to the proposed mechanism, surface basicity can be employed as a controlling parameter capable of tuning the adsorption capacity as well as the selectivity of CeO₂ towards organic pollutants.