Effect of Catalyst Preparation on Catalytic Activity

Effect of metal–support interactions in Ni/Al2O3 catalysts with low metal loading for methane dry reforming

“…On a specific basis, both catalysts converted similar amounts of carbon dioxide, and 2NiCA had a higher H 2 /CO ratio confirming that the types of sites affect activity and selectivity of the methane dry reforming reaction favoring different reaction pathways. It was shown that different surface nickel species exhibit different catalytic behavior, such as activity and mechanism for methanation of CO [20]. The higher H 2 /CO ratio for 2NiCA and the increase in methane conversion indicated that this catalyst could promote steam reforming of methane (reaction (3)) more effectively than 2NiDI (Fig.…”

“…However, one of the main problems with Ni/Al 2 O 3 catalysts with low nickel content is the formation of supposedly inactive nickel aluminate. In the literature, several common critical points with regards to the types of nickel species present on the alumina surface were identified: Oxidation at 500 • C was said to form stoichiometric and nonstoichiometric nickel aluminates [13], and nickel loadings below 1 wt% were said to produce only surface NiAl 2 O 4 [11,20]. In case of slightly higher weight loading (such as 2 wt%), different types of active sites (NiAl 2 O 4 and NiO) are expected to be present.…”

Heterogeneous hydrogenation catalysts

“…104 The limiting stage of the methanation is determined by the type of active centres prevalent on the surface. According to Huang and Schwarz, 47 the process of CO methanation includes the following stages: Investigation of the surface interaction of CO and H 2 on Ni/ Al 2 O 3 catalysts with variable Ni content by X-ray photoelectron spectroscopy (XPES), thermoprogrammed reaction (TPR) 113 and other methods confirmed that in the case of prevalence of NiAl 2 O 4 centres on the surface (catalysts with low Ni content) the methanation rate is determined by the rate of CO dissociation [stage (2)]. On catalysts with high Ni content, in which nickel is in the form of particles, the methanation rate is determined by that of hydrogenation of the CH x fragments [stage (8)].…”

“…On catalysts with high Ni content, in which nickel is in the form of particles, the methanation rate is determined by that of hydrogenation of the CH x fragments [stage (8)]. 47 If the reaction of methanation is regarded as being structure-sensitive, then the changes in its mechanism are well explained by the lower degree of Ni dispersity and the increase in its content from 0.8 mass % to 8.0 mass %.…”

X-ray diffraction study of the hydrogen reduction of NiO/α-Al2O3 steam reforming catalysts

“…Bartholomew and Farrauto explained these effects in terms of the chemistry of preparation, pretreatment and reduction conditions [31]. Later, based on a comprehensive study of preparation parameters, Schwarz and coworkers [32][33][34][35][36][37][38][39][40][41][42] advanced the theory that Al 3+ ions dissolve during impregnation at low pH and subsequently incorporate into crystallized NiO precursors [40]. Clause et al, however, demonstrated that NiO lattice parameters in coprecipitated hydrotalcite-type precursors remain unchanged and Ni-doped alumina phases exist on the surface of NiO, thereby imparting greater stability against sintering and resulting in lower reducibility [43].…”