Effects of Added K₂CO₃, CaCO₃ and BaCO₃ on the Activities and Selectivities of Raney Nickel Alloy Catalysts for Decomposition of Methanol

Abstract

Effects of added K₂CO₃, CaCO₃ and BaCO₃ on the activities and selectivities of the Raney nickel alloy catalysts prepared from Ni-Cu-Al alloy were examined. Addition of K₂CO₃, CaCO₃ and BaCO₃ was carried out by impregnation of the catalyst with K₂CO₃, Ca(CH₃COO)₂ and Ba(CH₃COO)₂ aq. soln., respectively, followed by calcination in air at 500°C. The improvement of selectivity toward decomposition of methanol and the suppression of dimethyl ether formation were observed for the basic metal carbonates added catalysts (Table 1). Methanol decomposition activities of the catalyst increased with increasing amount of the added basic metal carbonates and reached a maximum at an characteristic value of content for each carbonate (Figs.1, 2, 3). The enhacement of the activity by the addition of CaCO₃ and BaCO₃ was found to be due to an increase in active sites (Figs.1, 2). For these catalysts, the crystallite size of Ni-Cu alloy decreased with increasing amount of the added carbonates (Figs.1, 2). On the other hand, the addition of K₂CO₃ caused no increase in active surface area (Fig.3). It could be presumed that K modified the active sites to enhance the activity. The carbon deposition of the catalysts after reaction at 350°C for 30 h increased with the increase of added amount of the carbonates, except the low content regions of CaCO₃ and BaCO₃ (Table 1). Deactivation was significant for the catalysts on which a large amount of carbon (Fig.4) was deposited.