TiO₂-supported heteropoly acid catalysts for dehydration of methanol to dimethyl ether: relevance of dispersion and support interaction

Abstract

Two heteropoly acids (HPAs) with Keggin structures, namely, H 3 PW 12 O 40 (HPW) and H 4 SiW 12 O 40 (HSiW), have been deposited on TiO 2 and used as catalysts for the production of dimethyl ether (DME) from methanol. The catalysts have been prepared by incipient wetness impregnation of HPW and HSiW on TiO 2 with HPA loadings ranging between 0.9 and 9.0 Keggin units (KU) per square nanometer. The structure and acid properties of the final catalysts have been thoroughly characterized by N 2 adsorption-desorption isotherms, TGA, XRD, Raman spectroscopy, XPS, NH 3 adsorption isotherms, DRIFT and 1 H NMR. All catalysts exhibit very high DME productivities and high methanol conversion rates at temperatures as low as 413 K. The effect of the HPA loading on TiO 2 for the production of DME has been correlated with the structure and acid properties of the final catalyst. We find an optimum loading for both TiO 2 -supported HPW and HSiW of 2.3 KU nm −2 . At this level, both HPW and HSiW are well dispersed onto the support, thus permitting the access of methanol to the active acid sites. On the contrary, higher HPA loadings on TiO 2 result in the formation of larger HPA units that prevent the access of methanol to the inner acid sites within the HPA. On the other hand, HPA loadings below 2.3 KU nm −2 result in a strong interaction between the acid protons of the HPAs and the support, hence preventing the participation of such protons in the methanol dehydration reaction, which results in lower methanol conversion rates.

Kinetic Investigation of η-Al2O3 Catalyst for Dimethyl Ether Production

“…Development of new and cheap catalysts for MTD process on a large scale is of great interest. Usually, methanol is converted over solid catalyst either as simply dehydration, yielding DME and water, or as deep dehydration, producing hydrocarbons [22]. At the reaction conditions used [240-300 °C]; hydrocarbons products were hardly detected as a side reaction product [10].…”

Effect of hierarchical meso–macroporous alumina-supported copper catalyst for methanol synthesis from CO2 hydrogenation

“…The catalytic hydrogenation of CO 2 to methanol is considered one of the most promising processes because methanol can be used as an energy carrier for fuel cell application [1][2][3]. Moreover, methanol can be converted to dimethyl ether (DME) [4,5] which is considered as a feasible fuel for diesel engines [6,7], or into higher hydrocarbons according to methanol-to-olefins (MTO) process [8][9][10][11].…”

Synthesis of 5‐hydroxymethylfurfural from fructose and inulin catalyzed by magnetically‐recoverable Fe3O4@SiO2@TiO2–HPW nanoparticles

“…Since HPW is soluble in water and many organic solvents, it must be first immobilized on an insoluble support, such as SiO 2 , titanium dioxide (TiO 2 ), zeolite and/or active carbon, in order to make heterogeneous HPW catalysts . Some studies have shown that supported HPW catalysts might have similar or even higher activities, compared to bulk HPW, for catalyzing dehydration reactions . The slightly increased activities might be attributed to the adsorption of reactants on the supports, leading to the increased local reactant concentrations near HPW active sites .…”