Preparation of Ni/SiO₂ Catalyst by Chemical Fume Thermal Deposition

Abstract

Ni/SiO₂ catalysts were prepared by chemical fume thermal deposition. This preparation proceeded as follows. Nickel-salt/methanol solution was sprayed into a tubular reactor with vaporized SiCl₄ and air, and then the mixture was immediately pyrolyzed in a reactor whose temperature was controlled at 1573 K at the hottest point.
The apparent diameter of the catalyst produced was estimated by the BET method, and the diameter of NiO, d_{NiO, x}, was measured by XRD. The relationship between d_{NiO, x} and the relative viscosity of sprayed solution, η, was represented by the following equation under the present experimental conditions.
d_{NiO, x}=k (η^0.45) ⁿ
where n and k are different for each case; n=1.48, k=19 nm for the [Ni (NO₃) ₂ /CH₃OH+air+SiCl₄] system, n=1.48, k=32 nm for the [NiCl₂ /CH₃ OH + air + SiCl₄] system, n=0.64, and k=110 nm both for the [Ni (NO₃) ₂ CH₃OH+air] system and the [NiCl₂/ CH₃OH+air] system.
The apparent growth rate of the catalyst, γ_ap, is proportional to the molar fraction of Ni salt, χ.
γ_ap=k_apχ
The reactivity of the catalyst was examined by the methanation of carbon mono-xide as a model reaction. The results show that the activity (TOF) was one or two magnitudes higher than those of conventionally prepared impregnated catalysts.