Silicon carbide and alumina open-cell foams activated by Ni/CeO2-ZrO2 catalyst for CO2 methanation in a heat-exchanger reactor

Abstract

This work investigates and compares the performances over the CO2 methanation reaction of two structured catalysts based on high thermal conductivity silicon carbide (SiC) and low thermal conductivity alumina (Al2O3) 40 PPI Open Cell Foams. The active phase (25 wt%Ni/20 wt%CeO2-55 wt%ZrO2) was coated by the In Situ-Solution Combustion Deposition (IS-SCD) method with sequential steps to reach the desired catalyst loading (0.5 g/cm3) for both supports. TEM, SEM, XRD, TPR and adhesion tests were used to characterize the prepared structured catalysts. A bench-scale reactor (total inlet flow rate = 0,585–2,215 Nm3 h−1) with an integrated cooling system was used to carry out the catalytic tests, varying the Gas Hourly Space Velocity (12,420–47,027 h−1) at a constant reactant ratio (CO2:H2:N2 = 1:4:0.5). Air was used as a cooling medium both in counter- and co-current flow configuration. Temperature profiles along the reactor in axial and radial directions were registered, compared and discussed. The results show that the improved thermal management enhances the CO2 methanation reaction for both catalysts. For the investigated conditions, the SiC sample enabled a favourable temperature distribution due to its higher thermal conductivity, leading, also at the high space velocity (GHSV = 47,027 h−1) higher performances (χCO2 = 71.1%; SCH4 = 94.2%; FCH4,OUT = 260 NL h−1) compared to the Al2O3-based catalyst (χCO2 = 56.7%; SCH4 = 89.1%; FCH4,OUT = 202 NL h−1). Moreover, an operating pressure of 2.80 bar slightly improved the SiC catalysts performance: a CO2 conversion of 77.1% and a CH4 selectivity of 95,6% were obtained while the overall CH4 productivity increased up to 285 NL h−1 (12.1 NL h-1gcat.-1).