Effects of support and reaction pressure for the synthesis of dimethyl ether over heteropolyacid catalysts

Abstract

Dimethyl ether (DME) is an advanced second-generation biofuel produced via methanol dehydration over acid catalysts such as γ-Al 2 o 3 , at temperatures above 240 °C and pressures above 10 bar. Heteropolyacids such as tungstosilicic acid (HSiW) are Brønsted acid catalysts with higher DME production rates than γ-Al 2 o 3 , especially at low temperatures (140-180 °C). In this work, we show that the performance of supported HSiW for the production of DME is strongly affected by the nature of the support. TiO 2 and SiO 2 supported HSiW display the highest DME production rates of ca. 50 mmol DME /h/ g HSiW. Characterization of acid sites via 1 H-NMR, NH 3-isotherms and NH 3-adsrobed DRIFT reveal that HSiW/X have Brønsted acid sites, HSiW/TiO 2 showing more and stronger sites, being the most active catalyst. Methanol production increases with T until 200 °C where a rapid decay in methanol conversion is observed. This effect is not irreversible, and methanol conversion increases to ca. 90% by increasing reaction pressure to 10 bar, with DME being the only product detected at all reaction conditions studied in this work. The loss of catalytic activity with the increasing temperature and its increasing with reaction pressure accounts to the degree of contribution of the pseudo-liquid catalysis under the reaction conditions studied.

Direct Synthesis of Dimethyl Ether from CO2: Recent Advances in Bifunctional/Hybrid Catalytic Systems

“…as a strategy to enhance the activity of HPAs in the methanol dehydration reaction [117][118][119][120]. In particular, silicotungstic acid (H 4 SiW 12 O 40 , HSiW) supported on TiO 2 , SiO 2 , and ZrO 2 showed a high activity in this reaction, being more active than bulk HSiW [121]. This enhancement of catalytic activity was associated with the improvement in the accessibility of the methanol to the acid sites due to an improvement in the interchange between methanol and crystallization water.…”

“…This enhancement of catalytic activity was associated with the improvement in the accessibility of the methanol to the acid sites due to an improvement in the interchange between methanol and crystallization water. Operation at temperatures above 180 • C limits the access of the methanol to the bulk structure and, therefore, means the loss of the pseudoliquid behavior of HPAs [121]. TiO 2 -supported heteropoly acids (HPAs) also exhibited very high catalytic activities for the dehydration of methanol [118].…”

Increasing dimethyl ether production from biomass-derived syngasviasorption enhanced dimethyl ether synthesis

“…4 The direct synthesis of DME entails the use of two different catalytic phases, one for the synthesis of methanol from syngas and one for DME production. Cu-ZnO-Al 2 O 3 (CZA) materials are the benchmark catalysts for the synthesis of methanol from syngas, 13,16,17 whereas acidic solids such as g-Al 2 O 3 , 16,18 zeolites, 19,20 acidic oxides 21 or heteropolyacids [22][23][24][25] are the most active catalysts for the methanol dehydration to DME.…”

“…Cu dispersion and Cu surface area were determined from N 2 O chemisorption. First, a temperature-programmed reduction (TPR-t) was performed by subjecting the catalyst under study to a thermal treatment between 25…”

Effects of Zinc and Aluminum on the CuO Crystalline Size for Direct Dimethyl Ether Synthesis from Syngas

“…The direct synthesis of DME entails the use of two different catalytic phases, one for the synthesis of methanol from syngas and one for DME production. Cu-ZnO-Al 2 O 3 (CZA) materials are the benchmark catalysts for the synthesis of methanol from syngas [9][10][11], whereas acidic solids such as γ-Al 2 O 3 [12], zeolites [13,14], acidic oxides [15], or heteropolyacids [16][17][18][19] are the most active catalysts for methanol dehydration to DME. Cu o , or more likely the Cu/ZnO interphase, is considered as the active site for methanol production [20,21].…”