Effect of water and methanol concentration in the feed on the deactivation of In2O3-ZrO2/SAPO-34 catalyst in the conversion of CO2/CO to olefins by hydrogenation

Abstract

On account of the superior performance of In2O3-ZrO2/SAPO-34 tandem catalyst in the direct synthesis of olefins from CO, CO2 and CO/CO2 mixture by hydrogenation, it is interesting to establish the conditions to avoid its deactivation due to the rapid coke deposition on SAPO-34. The co-feeding of H2O and/or methanol together with H2 + CO2/CO was studied in a packed bed reactor at: 400 °C, 30 bar; CO2/COx in the feed, 0–1; H2/COx in the feed, 1–3; and space time of 5 gcat h molC−1, quantifying the evolution with time on stream (up to 16 h) of CO2 and COx conversions and olefin, paraffin and CH4 yields. The effects of the co-feeding on coke content and its nature were determined by temperature programmed oxidation (TPO) analyses of the spent catalyst. The results highlighted the complex effect of the concentration of H2O and oxygenates (methanol/dimethyl ether (DME)) on the deactivation of SAPO-34 and on the products yields in the pseudo-steady state of the catalyst. Co-feeding H2O lessens coke deactivation, however, high H2O concentration leads to attenuate the acidity of SAPO-34, limiting the performance of the tandem catalyst (mainly in the CO2 conversion). Oxygenates co-feeding concentration limit value lies on its favoring effect for coke formation. In addition to this effect, the favorable attenuation of coke deactivation by the high H2 concentration (studied in runs with H2/COx ratio in the feed in the 1–3 range) plays a key role in the viability of the process, leading to a pseudo-steady catalyst state in which the activity is constant. The proven effect of H2O and methanol concentrations will be useful for establishing new catalysts and reaction conditions at which their presence in the reactor will attenuate deactivation.