The Role of Ni Species Distribution on the Effect of Ce as a Promoter in C2-ODH Reaction

Abstract

The aim of work was to analyse and discuss the effect of cerium on the catalytic behaviour of different types of nickel species in the oxidative dehydrogenation of ethane. Ni-Al and Ni-Ce-Al catalysts were prepared from cerium nitrate and nickel nitrate or nickel acetate as a precursor. As-prepared materials were characterized by using of XRD, DR UV-Vis spectroscopy and H 2 -TPR. It was found that the addition of cerium affects both the reducibility of nickel species and the population of nickel species. Firstly, the addition of cerium led to the significant decrease of the reduction peak at 755-785°C to about 40°C due to the Ni-Ce interaction at both Ni-Ce-Al-NO 3 and Ni-Ce-Al-ac catalysts. Secondly, the addition of cerium affected the relative population of nickel species in tetrahedral and octahedral coordination, which population originated from used nickel precursor. The presence of cerium in Ni-Ce-Al-NO 3 catalysts led to the decrease in the relative population of Ni(T d ) species, while the crystal size of NiO in Ni-Ce-Al-ac catalysts decreased with increasing Ce/Ni ratio. The highest ethylene productivity was achieved on catalysts with Ce/Ni molar ratio 0.13. Catalysts exhibited an ethylene productivity up to 1.0 gC 2 =Ág cat -1 Áh -1 with a selectivity of 82 % (Ni-Ce-Al-NO 3 ) and 1.3 gC 2 =Ág cat -1 Áh -1 with a selectivity of 75 % (Ni-CeAl-ac).

Effect of Calcination Temperature on the Structure and Catalytic Performance of the Ni/Al2O3 and Ni–Ce/Al2O3 Catalysts in Oxidative Dehydrogenation of Ethane

“…They also reported that the structured systems show higher ethene productivity than the powder catalysts and that the catalytic features of the structured systems depend on the calcination temperature of the material . More recently, we reported that the distribution of Ni species and the catalytic behavior of Ni/Al 2 O 3 catalysts could also be affected by the type of nickel precursor (nickel nitrate vs nickel acetate) and by the Ce–Ni interaction . The results showed that Ni/Al 2 O 3 catalysts prepared by impregnation of alumina with nickel acetate contain higher relative populations of active small and dispersed NiO species, while the catalysts prepared by impregnation of alumina with nickel nitrate contain less active but more selective Ni­(T d ) species .…”

“…The fact that the presence of Ce as a promoter increases the activity of Ni/Al 2 O 3 catalysts is in agreement with previously reported results. 23,26 Nevertheless, this difference in W/F ratios (the change in the activity) obtained for Ni/Al 2 O 3 and Ni−Ce/Al 2 O 3 catalysts calcined at the same temperature decreased with an increasing value of calcination temperature. All these conclusions are the same as those described based on Figure 7.…”

“…23 More recently, we reported that the distribution of Ni species and the catalytic behavior of Ni/ Al 2 O 3 catalysts could also be affected by the type of nickel precursor (nickel nitrate vs nickel acetate) 25 and by the Ce−Ni interaction. 26 The results showed that Ni/Al 2 O 3 catalysts prepared by impregnation of alumina with nickel acetate contain higher relative populations of active small and dispersed NiO species, while the catalysts prepared by impregnation of alumina with nickel nitrate contain less active but more selective Ni(T d ) species. 25 In addition, the presence of the cerium promoter decreases the relative population of less active Ni(T d ) species in the Ni−Ce/Al 2 O 3 catalysts prepared by using nickel nitrate and decreases the crystallite size of NiO in the Ni−Ce/Al 2 O 3 catalysts prepared by using nickel acetate.…”

“…23 More recently, we reported that the distribution of Ni species and the catalytic behavior of Ni/ Al 2 O 3 catalysts could also be affected by the type of nickel precursor (nickel nitrate vs nickel acetate) 25 and by the Ce−Ni interaction. 26 The results showed that Ni/Al 26 In the present article we focused on the comparison of the catalytic behavior of supported Ni/Al 2 O 3 (cerium free) and Ni−Ce/Al 2 O 3 (presence of the cerium promoter) catalytic systems in oxidative dehydrogenation of ethane. The catalysts were prepared by the impregnation and the coimpregnation of nickel nitrate or nickel and cerium nitrates.…”

“…These effects enhanced the ethene productivity in ODH of ethane over both types of Ni−Ce/Al 2 O 3 catalysts, and the highest ethylene productivity was achieved on catalysts with a Ce/Ni molar ratio of 0.13. 26 In the present article we focused on the comparison of the catalytic behavior of supported Ni/Al 2 O 3 (cerium free) and Ni−Ce/Al 2 O 3 (presence of the cerium promoter) catalytic systems in oxidative dehydrogenation of ethane. The catalysts were prepared by the impregnation and the coimpregnation of nickel nitrate or nickel and cerium nitrates.…”