Oxidative conversion of methane to syngas over nickel supported on commercial low surface area porous catalyst carriers precoated with alkaline and rare earth oxides

Abstract

Partial oxidation of methane to CO and H₂ at very small contact times (4.8 ms at STP) over different supported Ni-catalysts at 700 and 800°C, CH₄/O₂ ratio in feed of 1.8 and gas space velocity of 5.2 × 10⁵cm³ .g^-1.h^-1(at STP) has been investigated. The catalysts were prepared by depositing NiO-MgO on different commercial low surface area porous catalyst carriers (obtained from M/S Norton Co., USA) consisting of refractory compounds (viz. SiO₂, Al₂O₃, SiC, ZrO₂, and HfO₂) at different concentrations and having different surface properties and also prepared by depositing NiO on the catalyst carriers precoated with different alkaline and rare earth oxides (viz. MgO, CaO, SrO, BaO, Sm₂O₃, and Yb₂O₃). The catalysts have been characterized by their TPR by H₂ from 100 to 900°C, degree of NiO reduction, and H₂ chemisorption after the catalyst reduction at 900°C. The influence of support (its composition and surface properties), method of NiO and MgO deposition, support precoating agent, loadings of NiO and MgO (as support precoating agent), and calcination temperature on the conversion and selectivity has been studied. The influence of these catalyst parameters on the TPR, degree of NiO reduction, and H₂ chemisorption on the catalyst has also been studied. The catalyst characteristics are strongly influenced by the support (containing Al₂O₃ and/or SiO₂ at higher concentrations and having higher surface area), precoating agent, loading of MgO precoat on the support, particularly at lower loadings (below 2 wt%), and also by the catalyst calcination temperature above 900°C. The catalyst prepared by depositing NiO on the commercial supports (except SA-5552 having much higher surface area) precoated with MgO (6 ± 1 wt%) and calcined at 900°C shows excellent performance in the catalytic process (at 800°C) with very high methane conversion (>91%), selectivity (>95%) and CO productivity (>13 mol.g^-1.h^-1, which is about two orders of magnitude higher than that obtained in steam reforming of methane). However, the conversion and selectivity are reduced drastically when the MgO loading is decreased below 2 wt%, the MgO precoat is replaced by that of SrO or BaO or when the catalyst is calcined above 1050°C.