Direct Synthesis of Dimethyl Ether from Syngas on Bifunctional Hybrid Catalysts Based on Supported H3PW12O40 and Cu-ZnO(Al): Effect of Heteropolyacid Loading on Hybrid Structure and Catalytic Activity

Abstract

The performance of bifunctional hybrid catalysts based on phosphotungstic acid (H3PW12O40, HPW) supported on TiO2 combined with Cu-ZnO(Al) catalyst in the direct synthesis of dimethyl ether (DME) from syngas has been investigated. We studied the effect of the HPW loading on TiO2 (from 1.4 to 2.7 monolayers) on the dispersion and acid characteristics of the HPW clusters. When the concentration of the heteropoliacid is slightly higher than the monolayer (1.4 monolayers) the acidity of the clusters is perturbed by the surface of titania, while for concentration higher than 1.7 monolayers results in the formation of three-dimensional HPW nanocrystals with acidity similar to the bulk heteropolyacid. Physical hybridization of supported heteropolyacids with the Cu-ZnO(Al) catalyst modifies both the acid characteristics of the supported heteropolyacids and the copper surface area of the Cu-ZnO(Al) catalyst. Hybridization gives rise to a decrease in the copper surface area and the disappearance of the strong acidic sites typical of HPW nanocrystals, showing all hybrids similar acid sites of weak or medium strength. The activity of the hybrids was tested for direct DME synthesis from syngas at 30 bar and 250 °C; only the hybrids with HPW loading higher than 1.4 monolayers showed activity for the direct synthesis of DME, showing that the sample loaded with 2.7 monolayers of heteropolyacid had higher activity than the reference hybrid representative of the most widely applied catalysts based on the combination of Cu-ZnO(Al) with HZSM-5. In spite of the high activity of the hybrids, they show a moderate loss in the DME production with TOS that denotes some kind of deactivation of the acidity function under reaction conditions.

Direct catalytic production of dimethyl ether from CO and CO2: A review

“…Activity tests were performed in a fixed-bed reactor loaded with hybrid catalysts diluted with SiC (1:3 vol). The overall methanol and DME yield on CZA-HPW/Ti hybrids was, in all cases, lower than the methanol yield achieved on the CZA reference [141].…”

Direct Synthesis of Dimethyl Ether on Bifunctional Catalysts Based on Cu–ZnO(Al) and Supported H3PW12O40: Effect of Physical Mixing on Bifunctional Interactions and Activity

“…The enhancement of activity of TiO 2 -supported HPA was associated with the good dispersion of H 3 PW 12 O 40 units on the TiO 2 surface, allowing easy access of methanol to the active acid sites. We have recently investigated H 3 PW 12 O 40 supported on TiO 2 combined with Cu/ZnO­(Al) catalyst as an active bifunctional catalyst for the direct synthesis of DME from syngas . The activity of this bifunctional catalyst was remarkably superior to that of the state-of-the-art Cu–ZnO­(Al)/HZSM-5 bifunctional catalyst commonly employed for DME production.…”

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

“…At this optimum loading, both HPW and HSiW were well dispersed onto the support surface, permitting the easy access of methanol to the active acid sites. The effect of supporting tungstophosphoric acid (H 3 PW 12 O 40 , HPW) on TiO 2 on the activity of a hybrid catalyst containing Cu-ZnO(Al) and HPW/TiO 2 as metal and acid functions, respectively, was investigated recently in the direct CO 2 hydrogenation to DME [122]. In good agreement with the study by Ladera et al [123], it was found that the amount of HPW employed for TiO 2 modification should be optimized.…”

“…Noticeably, the activities of this catalyst was higher than that of the reference hybrid Cu-ZnO(Al)/HZSM-5 catalyst, typically employed for DME production. However, the catalyst modified with an optimized amount of HPW exhibited some kind of catalyst deactivation under the reaction conditions employed [122].…”