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Graphical abstract Highlights • Oxidative dehydrogenation of n-butane depends on SiO 2 species and pore size. • The order of butadiene yield as SBA-15 > SiO 2 foam > MCM-41 > conventional silica. • The enhanced activity is related to active NiO on Bi 2 O 3-a (a = 0.2-0.4) phase. • The presence of strong basic with weak/moderate acid sites plays an important role. • The Bi 2 O 3-a phase serves as an active phase for dispersing NiO on the catalyst. Abstract Ni-Bi-O/structured mesoporous (MCM-41, SBA-15, and silica foam) silica catalyst with 20 wt% Ni and 30 wt% Bi has been studied in oxidative dehydrogenation of n-butane to butadiene. Mesoporous SBA-15 showed a clear superiority in activity and selectivity as compared to MCM-41, silica foam and conventional silica. The order of the butadiene yield was SBA-15 > Silica foam > MCM-41 > conventional silica. SBA-15 catalyst exhibits the best performance (butadiene selectivity: 47.5% at n-butane conversion: 28.9%) due to the presence of Bi 2 O 3-a phase (a = 0.2-0.4) as well as the strong base with weak/moderate acid sites, as evident from XRD and TPD analysis, respectively. The formation of Bi 2 O 3-a (a = 0.2-0.4) phase is related to the template effect of structurally ordered silica. [ABSTRACT FROM AUTHOR]

[Display omitted] • Highly-dispersed Ni based catalyst was synthesized by co-impregnation technique. • NiO-beta-Bi 2 O 3 -Bi 2 SiO 5 /SBA-15 catalyst showed good performance in n-butane oxidative dehydrogenation. • Its high selectivity was due to the formation degree of Bi 2 SiO 5 and beta-Bi 2 O 3 phases. • These phases enhance the reducibility and dispersion of the active Ni species. • The high metal-support interaction stabilizes the redox cycle of the active Ni species. NiO-beta-Bi 2 O 3 -Bi 2 SiO 5 /SBA-15 catalysts, containing 10−20 wt% Ni and 10−30 wt% Bi loaded as metal weight on mesoporous SiO 2 support (SBA-15), were utilized for the oxidative dehydrogenation of n-butane to butadiene, comparing from the viewpoint of Bi oxide phase and combination balance with Ni oxide and the support. Bi 2 SiO 5 and beta-Bi 2 O 3 phases change depending on Ni/Bi ratio. "Reverse core-shell" structure with uniform mesoporosity catalytically active for the oxidative dehydrogenation of n-butane to butadiene was successfully synthesized with semi-dry conversion method. The shell was formed as Bi 2 SiO 5 /SBA-15 by partially dissolving an array of silanol inside SBA-15 mesopores with impregnated bismuth nitrate. The Bi 2 SiO 5 of the shell was increased by co-impregnated nickel nitrate. The layered core faced to mesopore was formed as catalytically active NiO/beta-Bi 2 O 3 on the shell. The degrees of formation Bi 2 SiO 5 and beta-Bi 2 O 3 reflected in the butadiene selectivity through changing the reducibility and dispersion properties. The catalyst with moderate loading of 20 wt% Ni and 10 wt% Bi exhibited a high advantage in the n-butane conversion: 30 % and butadiene selectivity: 49 % at 450 °C compared to the less and excess loaded catalysts. The catalytic performance of other mesoporous silica support catalysts also changed differently depending on Bi 2 SiO 5 and beta-Bi 2 O 3 phases. [ABSTRACT FROM AUTHOR]