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

Abstract

We studied different preparation methods to synthesize a series of bifunctional hybrid catalytic systems for the direct synthesis of DME from syngas. The objective was to optimize the contact and interaction between the methanol synthesis catalyst and the methanol dehydration catalyst (Cu/ZnO/Al 2 O 3 and H 3 PW 12 O 40 supported on TiO 2 , respectively) by using different mixing methods (simple mixing, mixing−milling, suspension, and mixing−pressing). It has been found that the close contact between methanol synthesis and acidic functions is highly dependent on the degree of mixing of the two catalysts. In this respect, the hybrid catalyst prepared by mixing−pressing, which represents the closest contact, shows the strongest alterations in both catalytic functions. These modifications are associated with a decrease in copper surface area and a decrease in strong acid sites caused by the physical blocking of active sites or by cation exchange of the Cu 2+ /Zn 2+ species from Cu−ZnO(Al) and the H + from the H 3 PW 12 O 40 units. The activity results demonstrated that the mixing−pressing method leading to a closer contact between the two catalytic functions led to a very low dimethyl ether time yield compared to the other bifunctional catalysts prepared by less severe mixing methods (19.4 vs 205−335 μmol/min•g cat ). This work clearly indicates the importance of the mixing method in the synthesis of the hybrid catalyst to optimize the distance and interaction between the metal and acid sites.

From CO2 to DME: Enhancement through Heteropoly Acids from a Catalyst Screening and Stability Study

“…These results are in line with the findings of Navarro et al using CZA with P-HPA@TiO 2 in the StD reaction. 39 …”

“… 31 − 37 Navarro et al reported the effective use of bifunctional catalysts with heteropoly acid (HPA) coating in the direct DME synthesis from syngas. 38 , 39 For the StD reaction, even core–shell structured catalysts with an HPA-impregnated γ-Al 2 O 3 and a CZA core are reported. 40 Since Keggin-type polyacids have a well-defined structure with a footprint of estimated 1 nm 2 , the amount of Keggin units (KU) per surface area of carrier material can be calculated as Keggin unit loading (KU nm –2 ).…”

“…However, high proximity of surface-basic CtM and surface-acidic MtD catalysts can lower the catalyst system’s life span. 22 , 29 , 39 , 46 , 47 …”

Hydrogenation of CO2 to Valuable C2-C5 Hydrocarbons on Mn-Promoted High Surface Area Iron Catalysts

“…This is because high surface area bulk catalysts offer a larger number and a better arrangement of exposed active sites. However, although the positive effect of using highly ordered mesoporous catalysts for CO or CO2 hydrogenation reactions has been reported [26][27][28][29], there are also reports indicating that CO2 conversion may not be closely related to the structural properties of iron-based catalysts [20][21][22][23][24][25][26][27][28][29][30]. For example, a surprisingly high activity in CO2 hydrogenation showed an undoped bulk iron catalyst with a relatively low specific surface area (~30 m 2 .g -1 ) [20].…”

“…In addition to the catalyst composition, the catalyst preparation method and the structural property of the precursor agent are other important factors influencing the final catalyst performance in CO2 hydrogenation [22][23][24][25]. Most catalysts prepared for the conversion of CO2 to value-added hydrocarbons are synthesized by classical hydroxide coprecipitation followed by calcination.…”