Dehydration of methanol and ethanol in the gas phase over heteropoly acid catalysts

Dehydration of ethanol over heteropoly acid catalysts in the gas phase

Dehydration of methanol to dimethyl ether (DME) was studied at a gas/solid interface over a wide range of bulk and supported Bronsted acid catalysts based on tungsten Keggin heteropoly acids (HPA) and compared with the reaction over HZSM-5 zeolites (Si/Al = 10–120). Turnover rates for these catalysts were measured under zero-order reaction conditions. The HPA catalysts were demonstrated to have much higher catalytic activities than the HZSM-5 zeolites. A good correlation between the turnover rates and catalyst acid strengths, represented by the initial enthalpies of ammonia adsorption, was established. This correlation holds for the HPA and HZSM-5 catalysts studied, which indicates that the methanol-to-DME dehydration with both HPA and HZSM-5 catalysts occurs via the same (or similar) mechanism and the turnover rate of methanol dehydration for both catalysts is primarily determined by the strength of catalyst acid sites, regardless of the catalyst pore geometry.

Etherification of n-butanol to di-n-butyl ether was carried out over various structural classes of heteropolyacid (HPA) catalysts, including Keggin- (H3PW12O40), Wells-Dawson- (H6P2W18O62), and Preyssler-type (H14[NaP5W30O110]) HPA catalysts. Successful formation of HPA catalysts was well confirmed by FT-IR, 31P NMR, and ICP-AES analyses. Acid properties of HPA catalysts were determined by NH3-TPD (temperature-programmed desorption) measurements. Acid strength of the catalysts increased in the order of H14[NaP5W30O110] < H6P2W18O62 < H3PW12O40. The catalytic performance of HPA catalysts was closely related to the acid strength of the catalysts. In the etherification of n-butanol to di-n-butyl ether over various structural classes of HPA catalysts, Conversion of n-butanol and yield for di-n-butyl ether increased with increasing acid strength of HPA catalysts. Among the catalysts tested, Keggin-type (H3PW12O40) HPA catalyst with the strongest acid strength showed the best catalytic performance. Acid strength of HPAs served as an important factor determining the catalytic performance in the etherification of n-butanol to di-n-butyl ether.

Compensation effect in isopropanol dehydration over heteropoly acid catalysts at a gas–solid interface

Acidity of group 5 metal-substituted H4PW11M1O40 (M = V, Nb, Ta) Keggin and H7P2W17M1O62 (M = V, Nb, Ta) Wells-Dawson heteropolyacid (HPA) catalysts was measured by NH3-TPD experiment. Acidity of H4PW11M1O40 (M = V, Nb, Ta) and H7P2W17M1O62 (M = V, Nb, Ta) HPA catalysts showed the same trend with respect to polyatom substitution in both series of HPA catalysts. Vapor-phase esterification of acetic acid with ethanol was carried out as a model reaction to correlate the acidity with the acid catalysis of the HPA catalysts. Yield for ethyl acetate (a product formed by acid catalysis of HPA) over H4PW11M1O40 (M = V, Nb, Ta) and H7P2W17M1O62 (M = V, Nb, Ta) HPA catalysts increased with increasing acidity of the HPA catalysts, regardless of the identity of HPA catalyst. Acidity of H4PW11M1O40 (M = V, Nb, Ta) and H7P2W17M1O62 (M = V, Nb, Ta) HPA catalysts could be utilized as a probe of acid catalysis for esterification of acetic acid with ethanol. Vapor-phase esterification of acetic acid with ethanol was carried out over H4PW11M1O40 (M = V, Nb, Ta) Keggin and H7P2W17M1O62 (M = V, Nb, Ta) Wells-Dawson heteropolyacid (HPA) catalysts. Yield for ethyl acetate (a major product formed by acid catalysis of HPA) increased with increasing acidity of the HPA catalysts, regardless of the identity of HPA catalyst.

Etherification of n-butanol to di-n-butyl ether over H3PMo12−W O40 (x= 0, 3, 6, 9, 12) Keggin and H6P2Mo18−W O62 (x= 0, 3, 9, 15, 18) Wells–Dawson heteropolyacid catalysts

α-Pinene isomerisation over heteropoly acid catalysts in the gas-phase

Subject index

Dehydration of methanol and ethanol over silica-supported heteropoly acids in the gas phase: Surface-type versus bulk-type catalysis mechanism

Density Functional Theory Investigations of Zeolite and Intermetallic Alloy Active Site Structures for Kinetics of Heterogeneous Catalysis

Etherification of n-butanol to di-n-butyl ether over HnXW12O40 (X Co2+, B3+, Si4+, and P5+) Keggin heteropolyacid catalysts

Methanol dehydration catalysts in direct and indirect dimethyl ether (DME) production and the beneficial role of DME in energy supply and environmental pollution

Keggin-type heteropoly acids (HPAs) have strong Brønsted acidity and are widely used as acid catalysts. The aim of this work is the systematic characterisation of the acid strength of HPA catalysts comprising H3PW12O40 and H4SiW12O40 supported on SiO2, TiO2 and ZrO2 with 10–100% HPA loading and testing their activity in dehydration of alcohols to gain new mechanistic insight regarding the role of bulk-type and surface-type HPA catalysis in this reaction. The HPA catalysts were prepared by impregnation from an aqueous solution and characterised using BET, XRD, TGA, DRIFTS and ICP–OES. The acid strength of HPA catalysts was determined by NH3 adsorption microcalorimetry and found to decrease in the order HPA/SiO2 > HPA/TiO2 > HPA/ZrO2. For each type of HPA catalyst, the acid strength increased with increasing HPA loading. This can be attributed to HPA-support interaction reducing the strength of HPA proton sites at low HPA loadings. The activity of HPA catalysts was tested in the gas-phase dehydration of MeOH and i-PrOH in a fixed-bed reactor. Evidence was obtained that alcohol dehydration over HPA catalysts in a steady-state flow system occurs via the surface-type rather than bulk-type catalysis as suggested hitherto. This follows from a strong correlation between the reaction rate and the number of surface proton sites in HPA catalysts.

Direct preparation of dichloropropanol (DCP) from glycerol using heteropolyacid (HPA) catalysts: A catalyst screen study

Redox properties and oxidation catalysis of group 5 metal (V, Nb, Ta)-containing Keggin and Wells–Dawson heteropolyacid (HPA) catalysts