Comprehensive parametric assessment of steam-adsorption intensified hydrogenation of CO₂ to DME

Direct CO2-to-DME conversion on CuO-ZnO-Al2O3 (CZA) and PTA (phosphotungstic acid)/gamma-Al2O3 catalyst mixture is intensified by integrated H2O capture via Zeolite 3A (Z3A) adsorbent. The adsorbent-free experiments involving comparison of the PTA/gamma-Al2O3 and gamma-Al2O3 catalysts at 215-265 degrees C, 3 MPa, gas hourly space velocity (GHSV) = 1750 h(-1) and H-2:CO2:N-2 = 3:1:1 show that PTA integration allows > tenfold increase in the specific DME production rate which is maximized at 245 degrees C and CZA:PTA/gamma-Al2O3 mass ratio of 1:1. At these conditions, pressure swing adsorption assisted testing at all GHSV (5250, 7000, 10500 h(-1))/Z3A loading (2, 6, 10 g) combinations shows the clear trade-off between catalytic activity and productivity. CO2 conversion and DME selectivity are maximized at 5250 h(-1)/10 g Z3A due to increased contact time and H2O uptake capacity. However, peak productivity is observed at 7000 h(-1)/6 g Z3A because of shortened adsorbent regeneration. The role of acidity in the presence of sorption enhancement is highlighted by the similar to 75 % and similar to 19 % increases in DME selectivity and productivity, respectively, when the PTA/gamma-Al2O3 catalyst is used instead of gamma-Al2O3. The stability of the CZA + PTA/gamma-Al2O3 + Z3A system in driving intensified CO2 valorization to DME is demonstrated by the nearly identical reaction-regeneration cycles over 50 h.