Effect of Cobalt–Nickel ratio on the acid-base properties of Co–Ni/TiO2 catalysts via TPR and TPD analysis for steam reforming hydrogen production

Abstract

This study investigates the effect of cobalt incorporation on the acid-base properties of Co–Ni/TiO 2 catalysts with Co content ranging from 0 % to 15 wt%. The catalysts were characterized by XRD, BET, SEM, FTIR, H 2 -TPR, NH 3 -TPD, CO 2 -TPD, and TGA. Increasing cobalt content resulted in a decrease in surface area and pore volume, likely due to pore blockage by NiO and Co 3 O 4 particles. SEM confirmed particle size growth with higher Co levels. H 2 -TPR revealed stronger metal-support interactions at higher Co loadings. NH 3 -TPD indicated an increase in surface acidity, which may improve catalyst stability and reduce carbon deposition. However, CO 2 -TPD showed a decrease in basicity, suggesting reduced CO 2 adsorption and lower coking resistance. TGA results confirmed improved thermal stability at lower cobalt contents. Overall, cobalt significantly influences the structural, acid-base, and thermal properties of Co–Ni/TiO 2 catalysts. Two catalysts based on 5 %Co–10 %Ni/TiO 2 and 10 %Co–10 %Ni/TiO 2 were then tested in the steam methane reforming (SMR) reaction. Catalytic tests demonstrated that the 5 %Co–10 %Ni/TiO 2 catalyst offered the best performance with a methane conversion of 77.9 % and a hydrogen yield of 49.68 % at 700 °C and 2 bar, outperforming the 10 wt% Co catalyst, whose thermal stability was found to be inferior according to spent catalyst analyses (XRD, SEM and TGA). Increasing the H 2 O/CH 4 (S/C) ratio and the reaction temperature (up to 800 °C) improved the conversion and selectivity to H 2 and CO 2 while limiting CO formation. The results reveal that the 5 %Co–10 %Ni/TiO 2 catalyst exhibits good thermal stability with low carbon production compared to the second catalyst based on 10 %Co–10 %Ni/TiO 2 which showed poor thermal stability and higher carbon formation, highlighting the crucial importance of acid-base balance and metal dispersion in designing efficient and stable catalysts for the SMR process. • Increasing cobalt charge in Co–Ni/TiO 2 catalysts reduces pore surface area and volume, while increasing particle size. • Catalyst acidity increases with cobalt content, while basicity decreases, reducing CO 2 adsorption capacity. • Adding cobalt strengthens metal-support interaction and shifts reduction peaks to higher temperatures, altering structure. • The 5 %Co–10 %Ni/TiO 2 catalyst delivers optimal SMR performance at 700 °C with 77.9 % CH 4 conversion and 49.68 % H 2 yield. • Catalysts with less cobalt amount shows better thermal stability and resistance to coke.