Decomposition of Methanol over Raney Nickel Alloy Catalysts

Abstract

The preparative methods of the Raney-type catalysts for decomposition of methanol were examined. Ni-Al and Ni-Cu-Al alloys were used as catalyst raw materials.
The catalyst oxide precursors were prepared by leaching the Raney alloys w ith dilute NaOH aq. soln., followed by oxidation and calcination in air. Addition of Cu and K as promoter were carried out by impregnation of the oxide precursors with Cu²⁺ ammine complex ion and K₂CO₃ aq. soln., respectively. For Ni-Al₂O₃ catalyst prepared from Ni-Al alloy, low selectivity toward decomposition of methanol was observed, and extensive dea ctivation and carbon deposition occured. Addition of Cu, the constituents of resulting catalyst were copper-rich Ni-Cu alloy, Ni and η-Al₂O₃, was found to improve selectivity toward decomposition of methanol markedly and to reduce deactivation and carbon depositio n to some extent. For Ni-Cu-Al₂O₃ catalyst prepared from Ni-Cu-Al alloy which consists of nickel-rich Ni-Cu alloy, Cu and η-Al₂O₃, decomposition of methanol and formation of dimethyl ether were predominant. And deactivation due to reversible poisoning by reaction product and carbon deposition was observed (Fig.3). On the other hand, the deact ivation of the Cu added catalyst, as prepared by impregnation of Ni-Cu-Al₂O₃ precu rsor with Cu²⁺, was found to be due to reversible poisoning. And the activity of the cata lyst was higher than Ni-Cu-Al₂O₃ catalyst (Table 3). For the catalysts impregnated with K₂CO₃, the suppression of dimethyl ether formation and the elimination of reversi ble poisoning were observed (Fig.4). For the catalysts impregnated with Cu²⁺, carbon d eposition was suppressed.