Performance of modified H-ZSM-5 zeolite for dehydration of methanol to dimethyl ether

The conversion of methanol to dimethyl ether was carried out over various commercial zeolites and modified H-ZSM-5 catalysts to evaluate their catalytic performance. A series of commercially available zeolite samples were used for vapor-phase dehydration of methanol to DME. Catalyst screening tests were performed in a fixed-bed reactor under the same operating conditions (T = 300 °С, P = 16 barg, WHSV = 3.8 h⁻¹). It was found that all the H-form zeolite catalysts in this study were active and selective for DME synthesis. According to the experimental results MDHC-1 catalyst exhibited the highest activity in dehydration of methanol.After finding the most active catalyst, the H-MFI90 zeolite was modified with Na content varying from 0 to 120 mol%, via wet-impregnation method to further improve its selectivity. All of catalysts were characterized by BET, XRD, NH₃-TPD, ICP, TGA, SEM, FT-IR and TPH techniques. It was found that these materials affected activity of MDHC-1 zeolite by changing its acidity. Ultimately, among all the catalysts studied, Na₁₀₀-modified H-MFI90 zeolite exhibited optimum activity, selectivity and stability at methanol dehydration reaction.     

Preparation of CuY catalyst using CuCl2 as precursor for vapor phase oxidative carbonylation of methanol to dimethyl carbonate

Cu^IY catalyst was prepared by heating the mixture of CuCl₂ and acidic Y zeolite under flowing nitrogen and characterized by TG/DTG, XRD and elementary analysis techniques. The experimental result indicate that when the heating temperature was from 350 °C to 500 °C, the CuCl₂ of the CuCl₂ and acidic Y zeolite mixture sample decompose to CuCl and Cl₂ gas, then the produced CuCl reacted with the Brønsted acid center H⁺ of Y zeolite to form Cu^IY catalyst by the solid-state ion-exchanged reaction. The amount of ion-exchanged Cu^I in the Cu^IY catalyst reached the maximum of 0.1 mol/g when the heating temperature was 650 °C, and the catalyst exhibited the best catalytic activity, the conversion of methanol (C_MeOH), the selectivity and the space-time yield of dimethyl carbonate (S_DMC and STY) reached 4.36%, 74.55% and 97.32 mg/(g h), respectively.     

Titanium-doped alumina for catalytic dehydration of methanol to dimethyl ether at relatively low temperatures

Mesoporous Al-Ti oxide composites with molar %Ti of 3, 5, 10, and 20 as well as pure γ-alumina were prepared using a template-free sol-gel method in the absence of a catalyst. The prepared composites were characterized by powder XRD, FTIR spectroscopy and N₂ adsorption for BET surface area and porosity measurements. The composites and the pure alumina possessed relatively high surface areas, 350-410 m²/g, and high porosities after calcination at 500 °C. FTIR spectroscopy was employed to study the products of the catalytic dehydration of methanol to dimethyl ether, DME, over the prepared catalysts at reaction temperatures between 180 and 300 °C. Compared with pure γ-alumina, the Ti-modified alumina with %Ti < 10 showed higher catalytic activity in the methanol dehydration and better selectivity to DME. Composites with %Ti of 3 and 5 showed the highest activity at relatively lower temperatures than the other catalysts where they showed their highest activity at 190 and 200 °C, respectively. The activity of all studied catalysts slightly decreased as the temperature was raised to 300 °C and dropped considerably when the temperature was decreased to 180 °C. However, the activity of Al-Ti-3 dropped only slightly at both temperatures. The selectivity to DME was dependent on the reaction temperature where 100% DME selectivity was obtained at temperatures ?220 °C and as the temperature was raised to 300 °C, some CH₄ and CO₂ formed on the account of DME.     

Catalytic conversion of chloromethane to methanol and dimethyl ether over mesoporous γ-alumina

Mesoporous γ-alumina, mp-γ-Al₂O₃, possessing surface area around 385 m²/g and total pore volume of 2.0 cm³/g was prepared via template-free sol-gel synthesis. The catalytic activity of the prepared alumina for the conversion of chloromethane to dimethyl ether, DME, in the presence of water or methanol was studied in the temperature range of 170-450 °C employing FTIR spectroscopy. In the absence of water and methanol, the fresh surface of mp-γ-Al₂O₃ showed 100% conversion of chloromethane to DME at temperatures between 250 and 350 °C. However, rapid deactivation of the catalyst resulted in a sharp decrease in the conversion to < 5% within a few minutes of reaction. The catalytic activity was noticeably enhanced by adding water vapor to the gas feed resulting in higher conversions to DME and methanol. The catalytic activity and DME selectivity were further enhanced in the presence of methanol instead of water. In the temperature range of 200-300 °C, complete conversions were obtained at the beginning of reactions before they declined to values between 31 and 45% depending on the reaction temperature. It was proposed that the surface hydroxyl groups are the active sites where chloromethane molecules dissociatively adsorb forming adsorbed methoxy ion intermediates. The adsorption of molecular methanol regenerates the surface hydroxyl groups and enhances the formation of adsorbed methoxy ions on the surface which react further with chloromethane or methanol molecules to produce more DME.     

Synthesis of AlOOH slurry catalyst and catalytic activity for methanol dehydration to dimethyl ether

AlOOH slurry catalysts were prepared by complete liquid-phase technology from aluminum iso-propoxide (AIP). Dehydration of methanol to dimethyl ether (DME) over these catalysts was investigated in slurry reactor. The catalysts were characterized by X-ray diffraction (XRD), nitrogen adsorption, temperature-programmed desorption of ammonia (NH₃–TPD). The results showed that the slurry catalysts had high specific surface area and pore volume, and the specific surface area and the strength of weak acidic sites were influenced considerably by the molar ratio of H₂O/AIP and HNO₃/AIP. Activity tests indicated that AlOOH slurry catalysts had excellent catalytic activity and stability in slurry reactor for the dehydration of methanol to dimethyl ether, and the activity correlated well with the strength of weak acidic sites of catalysts, which can be controlled by changing the H₂O/AIP and HNO₃/AIP molar ratios. The average methanol conversion at even stage reaches nearly 80% and DME selectivity almost 100% over CAT-P1 catalyst. No deactivation was found during the reaction of 500 h. It is also expected that CAT-P1 becomes a promising methanol dehydration catalyst for the STD process based on CuZuAl methanol synthesis catalyst.     

High porous carbon with Cu/ZnO nanoparticles made by the pyrolysis of carbon material as a catalyst for steam reforming of methanol and dimethyl ether

Cu/ZnO/carbon catalysts for steam reforming reactions were prepared by the technique to obtain much amount of metals highly dispersed on the porous carbon. The preparation method includes the carbonization of an ion exchange resin loaded with metal cations. By containing ZnO in the resin, the agglomeration of Cu particle during the carbonization was suppressed within the carbon matrix due to the difference in the behavior of carbonization and migration between Cu and Zn in the same ion exchange resin, and the Cu particle size was reduced. Thus, the obtained Cu3Zn1 catalyst had more than double the Cu surface area of the catalyst contained only Cu, regardless of lower Cu content. Methanol steam reforming test showed that the catalysts’ activity was positively correlated with Cu surface area. Also in dimethyl ether (DME) steam reforming reactions using the composite catalysts with γ-Al₂O₃, the catalytic activity tracked with the surface area covered by Cu. The optimized Cu/ZnO/carbon catalyst composite showed a high DME conversion of 0.87 even at the low temperature of 300 °C and with GHSV = 2000 h⁻¹, which was due to high dispersion of Cu on the micropore structure of carbon support.     

Novel methanol electro-oxidation catalyst assisting with functional phthalocyanine supports

Novel electro-catalyst based on phthalocyanine stabilized Pt colloids has been developed for methanol electro-oxidation. Water soluble Cu²⁺ phthalocyanine functioned with sulfonic groups were selected as catalyst supports because of the relatively high catalytic activity of Pt catalyst and nearly the same catalytic selectivity complex with Cu-phthalocyanine, compared to others that chelated with Fe, Co and Ni ions. The as-resulting Pt-CuTsPc catalysts have average particle size of 2 nm and narrow size distribution. With the assistance of CuTsPc supports, the methanol electro-oxidation activity and poison tolerance of Pt catalyst have a significant increase. I_f/I_b ratio (anodic peak current density, forward to backward) of the Pt-CuTsPc/C catalysts also has obvious increase to 2.5, from value of 0.8 for pure Pt/C catalyst. The reaction Tafel slope of Pt-CuTsPc/C catalysts is 56.6 mV dec⁻¹, much smaller than that of the Pt/C catalyst. The transient current density on Pt-CuTsPc/C at 0.60 V is enhanced to 650% of that on the Pt/C catalyst while the enhancement factor R for comparison of steady-state current obtained on Pt-CuTsPc/C and Pt/C catalyst varies between 111% and 534% in the potential region of 0.3-0.75 V.     

Radioisotopic tracing of methanol transformation using 11C-labelled methanol over copper ion-exchanged H-ZSM-5, H-Beta and H-MCM-41

Short half-life ¹¹C-radioisotope tracer in methanol form was used to study the transformation of methanol over copper ion-exchanged H-ZSM-5, H-Beta and H-MCM-41 catalysts. The progresses of adsorption and desorption as well as methanol transformation were followed by radiodetection. The reaction products were analyzed by radio-gas chromatography. The GC analysis was completed with a radiodetector that could distinguish the radiolabelled derivates from other non-radioactive compounds, reagents or impurities. The radiodetector can be more sensitive to detect smaller amount of compound than the thermal conductivity detector or flame ionization detector since the intensity of a radio-signal is independent on thermal conductivity or ionization energy of compounds. The copper introduction into the catalysts had an inhibitory effect on the reaction to proceed further from the equilibration with the methanol and dimethyl ether resulting in hydrocarbons C₃–C₆. Presence of copper also allowed a possible reaction route for methanol to give formaldehyde and methyl formate.     

Selectivities in methanol oxidation over silica supported molybdena

Selectivities in methanol oxidation over silica supported molybdenum oxide catalysts were investigated in relation with the phase distribution. The supported catalysts were prepared by impregnation with ammonium heptamolybdate. In addition to crystalline MoO₃, Mo containing cluster species of 1–2 nm size were observed by STEM even from a used catalyst with 13% catalyst loading. The percentage of Mo present as crystalline MoO₃ increases with the catalyst loading. An ESCA study indicates that part of surface Mo in the supported catalysts is reduced to Mo⁵⁺. The dimethyl ether selectivity increases with the catalyst loading and its formation occurs over the crystalline MoO₃ phase. The Selectivities to CO and methyl formate are greatly enhanced because of the presence of support, and are relatively independent of the catalyst loading and phase distribution. The dependence and independence of the Selectivities of different byproducts on the loading make the silica supported catalysts with high catalyst loadings less selective for the partial oxidation of methanol to formaldehyde.     

Electroreduction of dioxygen (ORR) in alkaline medium on Ag/C and Pt/C nanostructured catalysts—effect of the presence of methanol

Ag/C catalysts with different loading were prepared using a colloidal route to obtain well dispersed catalysts on carbon, with a particle size close to 15 nm. An amount of 20 wt.% Ag on carbon was found to be the best loading in terms of current density and mass activity. The 20 wt.% Ag/C catalyst was then studied and the kinetics towards ORR was determined and compared with that of a 20 wt.% Pt/C catalyst. The number of exchanged electrons for the ORR was found to be close to four with the rotating disk electrode (RDE) as well as with the rotating ring disc electrode (RRDE) techniques. From the RDE results, the Tafel slopes b, the diffusion limiting current density inside the catalytic film (j_l^film) and the exchange current density (j₀) were evaluated. The Tafel slopes b and diffusion limiting current densities inside the catalytic film (j_l^film) were found to be in the same order for both catalysts, whereas the exchange current density (j₀), which is a suitable estimation of the activity of the catalyst, was at least 10 times higher at the Pt/C catalyst than at the Ag/C catalyst. The behavior of both catalysts in methanol containing electrolyte was investigated and it was found that at a low methanol concentration, the Pt/C catalyst was quasi-tolerant to methanol. But, at a high methanol concentration, the ORR at a Pt/C was affected. However, the Pt/C catalyst showed in each case better activity towards ORR than the Ag/C catalyst, even if the latter one was less affected by the presence of methanol than the former one.     

Nanocrystalline gamma-alumina: A highly active catalyst for dimethyl ether synthesis

In this article, mesoporous nanocrystalline γ-Al₂O₃ with high surface area is synthesized by a simple sol-gel method with cationic surfactant as template. This sample is used for vapor-phase dehydration of methanol to Dimethyl ether. The synthesized catalyst showed a high surface area of 375 m² g^− 1 and a crystallite size of about 3.9 nm. NH₃-TPD analysis revealed that the sample with smaller crystallite size possesses higher concentration of medium acidic sites and consequently the catalytic activity.     

CoPdx oxygen reduction electrocatalysts for polymer electrolyte membrane and direct methanol fuel cells

The electrochemical activity of carbon-supported cobalt-palladium alloy electrocatalysts of various compositions have been investigated for the oxygen reduction reaction in a 5 cm² single cell polymer electrolyte membrane fuel cell. The polarization experiments have been conducted at various temperatures between 30 and 60 °C and the reduction performance compared with data from a commercial Pt catalyst under identical conditions. Investigation of the catalytic activity of the CoPd_x PEMFC system with varying composition reveals that a nominal cobalt-palladium atomic ratio of 1:3, CoPd₃, exhibits the best performance of all studied catalysts, exhibiting a catalytic activity comparable to the commercial Pt catalyst. The ORR on CoPd₃ has a low activation energy, 52 kJ/mol, and a Tafel slope of approximately 60 mV/decade, indicating that the rate-determining step is a chemical step following the first electron transfer step and may involve the breaking of the oxygen bond. The CoPd₃ catalyst also exhibits excellent chemical stability, with the open circuit cell voltage decreasing by only 3% and the observed current decreasing by only 10% at 0.8 V over 25 h. The CoPd₃ catalyst also exhibits superior tolerance to methanol crossover poisoning than Pt.     

Catalytic activity of titanium oxide for oxygen reduction reaction as a non-platinum catalyst for PEFC

A non-platinum cathode electrocatalyst must have the stability and catalytic activity for the oxygen reduction reaction (ORR) in order to be used in polymer electrolyte fuel cells (PEFCs). Titanium oxide catalysts as the non-platinum catalyst were prepared by the heat treatment of titanium sheets in the temperature range from 600 to 1000 °C. The prepared catalysts were chemically and electrochemically stable in 0.1 mol dm⁻³ H₂SO₄. The titanium oxide catalysts showed different catalytic activities for the ORR. The ORR of the catalysts heat-treated at around 900 °C occurred at the potential of about 0.65 V versus RHE. It is considered that the deference in the catalytic activity for the ORR of the heat-treated titanium oxide catalysts was due to the fact that the heat-treatment condition changed the material property of the catalyst surface. In particular, it was found that the catalytic activity for the ORR of the Ti oxide catalysts increased with the increase in the specific crystalline structure, such as the TiO₂ (rutile) (1 1 0) plane and the work function. It is considered that a surface state change, such as the crystalline structure and work function, might affect the catalytic activity for the ORR.     

Effect of heat treatment on the performance of TiO2-Pt/CNT catalysts for methanol electro-oxidation

TiO₂-Pt/CNT catalysts before and after heat treatment were prepared. Their catalytic activities for methanol and CO electro-oxidation were studied in detail. The results showed that the proper amount of hydrous TiO₂ in TiO₂-Pt/CNTs (e.g. heated at 200 °C for 2 h) was favorable for enhancing the catalytic activity of Pt/CNTs, which provided evidence for bi-functional mechanism. The studies on the catalysts with different TiO₂/Pt molar ratio displayed that the optimum molar ratio varied with the increase of heat treatment temperature. It was found that the optimum molar ratio of TiO₂/Pt was at 1:2 for the catalysts without heat treatment and was at 1:1 for the catalysts by heat treatment at 500 °C. This fact was ascribed to the difference in compact degree between TiO₂ and Pt/CNTs before and after heat treatment. Considering the influence of heating temperature, it was found that TiO₂-Pt/CNT catalyst heated at 200 °C for 2 h had better catalytic activity for methanol oxidation.     

Hydrogen production by oxidative steam reforming of methanol using ceria promoted copper–alumina catalysts

The performance of different Cu/CeO₂/Al₂O₃ catalysts of varying compositions is investigated for the oxidative steam reforming of methanol (OSRM) in order to produce the hydrogen selectively for polymer electrolyte membrane (PEM) fuel cell applications. All the catalysts were prepared by co-precipitation method and characterized for their surface area, pore volume and oxidation–reduction behavior. The effect of various operating parameters studied are as follows: reaction temperature (200–300 °C), contact-time (W/F = 3–15 kg_cat s mol^− 1) and oxygen to methanol (O/M) molar ratio (0–0.5). The steam to methanol (S/M) molar ratio = 1.5 and pressure = 1 atm were kept constant. Among all the catalysts studied, catalyst Cu–Ce–Al:30–20–50 exhibited 100% methanol conversion and 179 mmol s^− 1 kg_cat^− 1 hydrogen production rate at 280 °C with carbon monoxide formation as low as 0.19%. The high catalytic activity and hydrogen selectivity shown by ceria promoted Cu/Al₂O₃ catalysts is attributed to the improved specific surface area, dispersion and reducibility of copper which were confirmed by characterizing the catalysts through temperature programmed reduction (TPR), CO chemisorption, X-ray diffraction (XRD) and N₂ adsorption–desorption studies. Reaction parameters were optimized in order to produce hydrogen with carbon monoxide formation as low as possible. The time-on-stream stability test showed that the Cu/CeO₂/Al₂O₃ catalysts were quite stable.     

The interaction effects of dehydration function on catalytic performance and properties of hybrid catalysts upon LPDME process

Three bi-functional catalysts have been prepared by physical mixing of a commercial methanol synthesis catalyst (CuO–ZnO–Al₂O₃) with three different methanol dehydration catalysts including: H-MFI90, γ-Al₂O₃ and H-Mordenite in order to investigate the role of interaction effects of dehydration component on characteristic properties and performance of these admixed catalysts. The bi-functional catalysts have been characterized by XRD, N₂ adsorption, H₂-TPR, NH₃-TPD and XRF techniques and tested in a mixed slurry bed reactor at the same operating conditions (T = 240 °C, P = 50 bar, H₂/CO = 2, SV = 1100 ml g-cat^− 1 h^− 1) for 60 h time on stream. Among the examined bi-functional catalysts, the physical mixture of KMT + HMFI-90, which had lower reducing peak temperature (T = 200 °C), higher S_Cu (39.1 m² g-cat^− 1) and Cu Dispersion (11.6%), showed higher X_CO (84 mol%), yield of DME (Y_DME = 55.5 mol%), DME selectivity (Select_DME = 66.7 mol%) and also good stability over 60 h time on stream as compared to the other catalysts. This could be assigned, from NH₃-TPD results, to more middle strength acidic sites of H-MFI90 zeolite (SiO₂/Al₂O₃ = 90, total acid site density = 476 µmol/g-cat) which inhibits detrimental interactions with methanol synthesis catalyst and deep dehydration of methanol.     

Preparation of CuCl/C catalyst for the synthesis of dimethyl carbonate: Effects of calcination temperature

Activated carbon supported cuprous chloride, a rarely examined catalyst, was prepared and applied to the oxidative carbonylation of methanol. The catalyst was prepared by impregnation. Water insoluble cuprous chloride was dissolved in hydrochloric acid. The effects of the calcination temperature in preparing the catalysts were examined. The results showed that, as the temperature was increased, the major surface species in the catalyst shifted from CuCl₃²⁻ to CuCl, then to Cu₂Cl(OH)₃, and finally to Cu⁰. Cuprous chloride appeared to be the active species for the production of dimethyl carbonate (DMC), and maximum amount of cuprous chloride in the catalyst occurred at a calcination temperature of 300 °C.     

Characterization and electrocatalytic properties of PtRu/C catalysts prepared by impregnation-reduction method using Nd2O3 as dispersing reagent

A simple impregnation-reduction method introducing Nd₂O₃ as dispersing reagent has been used to synthesize PtRu/C catalysts with uniform Pt-Ru spherical nanoparticles. X-ray diffraction (XRD) analysis, transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) analysis have been used to characterize the composition, particle size and crystallinity of the catalysts. Well-dispersed catalysts with average particle size about 2 nm are achieved. The electrochemically active surface area of the different PtRu/C catalysts is determined by the CO_ad-stripping voltammetry experiment. The electrocatalytic activities of these catalysts towards methanol electrooxidation are investigated by cyclic voltammetry measurements and ac impedance spectroscopy. The in-house prepared PtRu/C catalyst (PtRu/C-03) in 0.5 M H₂SO₄ + 1.0 M CH₃OH at 30 °C display a higher catalytic activity and lower charge-transfer resistance (R_t) than that of the standard PtRu/C catalyst (PtRu/C-C). It is mainly due to enhanced electrochemically active specific surface, higher alloying extent of Ru and the abundant Pt⁰ and Ru oxides on the surface of the PtRu/C catalyst.     

Effect of reduction conditions on electrocatalytic activity of a ternary PtNiCr/C catalyst for methanol electro-oxidation

The effect of reduction conditions on a Pt₂₈Ni₃₆Cr₃₆/C catalyst was investigated by using two different reduction methods: hydrogen reduction and NaBH₄ reduction. In hydrogen reduced catalysts, dissolution of metallic Ni and Cr was observed during cyclic voltammetry (CV) tests, and a larger amount of Ni and Cr was dissolved when reduced at higher temperatures. For methanol electro-oxidation, the highest specific current density of 1.70 A m⁻² at 600 s of the chronoamperometry tests was observed in the catalyst reduced at 300 °C, which was ∼24 times that of a Pt/C catalyst (0.0685 A m⁻²). In NaBH₄ reduced catalysts, formation of an amorphous phase and a more Pt-rich surface was observed in X-ray diffraction and CV results, respectively, with increasing amounts of NaBH₄. When reduced by 50 times of the stoichiometric amount of NaBH₄, the PtNiCr/C catalyst (PtNiCr-50t) showed a current density of 34.1 A g_{noble metal}⁻¹, which was 81% higher than the 18.8 A g_{noble metal}⁻¹ value of a PtRu/C catalyst at 600 s of the chronoamperometry tests. After 13 h of chronoamperometry testing, the activity of the PtNiCr-50t (15.0 A g_{noble metal}⁻¹) was 110% higher than the PtRu/C catalyst (7.15 A g_{noble metal}⁻¹). The PtNiCr/C catalyst shows promise as a Ru-free methanol oxidation catalyst.     

Comparative study of CO and CO2 hydrogenation over supported Rh–Fe catalysts

The hydrogenation of CO, CO + CO₂, and CO₂ over titania-supported Rh, Rh–Fe, and Fe catalysts was carried out in a fixed-bed micro-reactor system nominally operating at 543 K, 20 atm, 20 cm³ min^− 1 gas flow (corresponding to a weight hourly space velocity (WHSV) of 8000 cm³ g_cat^− 1 h^− 1), with a H₂:(CO + CO₂) ratio of 1:1. A comparative study of CO and CO₂ hydrogenation shows that while Rh and Rh–Fe/TiO₂ catalysts exhibited appreciable selectivity to ethanol during CO hydrogenation, they functioned primarily as methanation catalysts during CO₂ hydrogenation. The Fe/TiO₂ sample was primarily a reverse water gas shift catalyst. Higher reaction temperatures favored methane formation over alcohol synthesis and reverse water gas shift. The effect of pressure was not significant over the range of 10 to 20 atm.