Akademik Veri Yönetim Sistemi
ACS SUSTAINABLE CHEMISTRY & ENGINEERING, cilt.14, ss.5650-5663, 2026 (SCI-Expanded, Scopus)
The direct hydrogenation of CO2 to dimethyl ether (DME) is studied using physically mixed bifunctional catalysts composed of conventional CuO/ZnO/Al2O3 (CZA, for methanol synthesis) and phosphotungstic acid (H-3[P(W3O10)(4)]& centerdot;xH(2)O, PTA)-modified gamma-Al2O3 (for methanol dehydration to DME). A 30 wt % PTA loading and calcination at 500 degrees C optimizes the Br & oslash;nsted-to-Lewis acid site ratio and total acid site density, confirmed by NH3-TPD and in situ FTIR analyses of pyridine adsorption. Structural characterization reveals a disordered PTA overlayer on gamma-Al2O3 at 500 degrees C, which transforms into ordered WO3 and W18P2O59 domains at higher temperatures, leading to decreased Br & oslash;nsted acidity and lower catalytic performance. Methanol adsorption on the optimized catalyst is examined using in situ FTIR spectroscopy to shed light on the catalytic dehydration of methanol to DME. Methanol dehydration proceeds without the formation of formate intermediates, thus suppressing the generation of side products other than DME, and suggesting a Br & oslash;nsted acid-mediated associative, direct concerted mechanism. TPD analyses further confirm suppressed methanol dehydrogenation and limited byproduct formation (e.g., formic acid and CO), supporting a direct DME-formation pathway on the Br & oslash;nsted acid-enriched catalyst. Under optimized reaction conditions (245 degrees C, 3 MPa, CZA/acid catalyst mass ratio = 1/1), the CZA+PTA/gamma-Al2O3 catalyst achieves a CO2 conversion of 21.4%, a DME yield of similar to 12%, and a DME productivity of 6.9 & times; 10(-3) kg(DME) kg(cat)(-1) h(-1) corresponding to more than twice that of the benchmark CZA+gamma-Al2O3 system. Stability tests over 72 h reveal similar to 8% deactivation, which decreases to <3% at 48-72 h, confirming good hydrothermal durability. These results highlight that tuning the surface acidity and structural properties of gamma-Al2O3 via PTA incorporation, in combination with a conventional CZA catalyst, provides a robust platform for efficient low-temperature CO2-to-DME conversion.