CH3OH Selectivity Research Articles

Cu/Zn/Al/Zr catalysts via phase-pure hydrotalcite-like compounds for methanol synthesis from carbon dioxide

Cu/Zn/Al/Zr catalysts with Cu2+:Zn2+:Al3+:Zr4+=2:1:x:0.1 (x=0.6–1.5) were prepared from hydrotalcite-like precursors by co-precipitation method and tested for the CO2 hydrogenation to methanol. Both Cu/Zn/Al/Zr hydrotalcite-like and malachite phase were formed at low Al content. However, with the increase of Al content, the yield of hydrotalcite-like phase increased and phase-pure Cu/Zn/Al/Zr hydrotalcite-like compound was obtained for x≥0.9. In addition, both the specific surface area and the dispersion of Cu increased gradually with the increase of Al, while the exposed Cu surface area first increased until Al content was 27.9mol%, then decreased. The results of catalytic test for CO2 hydrogenation revealed that Cu/Zn/Al/Zr catalysts via phase-pure hydrotalcite-like compounds exhibited much better catalytic performance with higher CO2 conversion and CH3OH selectivity compared with the catalyst derived from mixed phase (hydrotalcite-like and malachite). The Cu/Zn/Al/Zr catalysts with Cu2+:Zn2+:Al3+:Zr4+=2:1:1.2:0.1 resulting from phase-pure hydrotalcite-like precursors afforded the substantial stability and the best catalytic performance.

Partial Oxidation of Methane to Methanol Using Bismuth-Based Photocatalysts

Bismuth-based photocatalysts, Bi2WO6, BiVO4, and coupled Bi2WO6/TiO2–P25, have been synthesized by a facile hydrothermal method, characterized, and evaluated for the first time for the selective photooxidation of methane to methanol. Several conditions were used in order to better comprehend the reaction mechanism. The obtained BiVO4 is, among the others, the most promising photocatalyst for this reaction, displaying higher CH3OH selectivity and being more stable than the others. When Bi2WO6 was coupled with TiO2, the methane conversion increased; however, overoxidation of CH4 to CO2 predominates. A similar effect is observed when electron scavengers such as O2 or Fe3+ were introduced in the photoreactor as a result of the formation of highly oxidant radicals.

Fluorine-modified Cu/Zn/Al/Zr catalysts via hydrotalcite-like precursors for CO2 hydrogenation to methanol

Fluorine-modified Cu/Zn/Al/Zr catalysts were prepared by calcination of the fluorine-containing Cu/Zn/Al/Zr hydrotalcite-like compounds and tested for CO2 hydrogenation to methanol. The results revealed that the CH3OH selectivity was greatly improved by the remarkable increase of the proportion of strongly basic sites, while the CO2 conversion decreased slightly. It is also found that the activity of catalysts is closely related to the synergy between the Cu and basic sites. The CH3OH yield for the fluorine-modified Cu/Zn/Al/Zr catalysts was higher than that for the fluorine-free catalysts; thus, the introduction of fluorine favored the methanol formation.

Influence of modifier (Mn, La, Ce, Zr and Y) on the performance of Cu/Zn/Al catalysts via hydrotalcite-like precursors for CO2 hydrogenation to methanol

A series of promoted Cu/Zn/Al catalysts derived from hydrotalcite-like precursors were synthesized by co-precipitation method and tested for the CO2 hydrogenation to methanol. The influence of modifier (Mn, La, Ce, Zr and Y) on the physicochemical properties of Cu/Zn/Al catalysts was studied in detail. The results show that the BET specific surface area, Cu surface area and Cu dispersion increase in the order of Cu/Zn/Al<Cu/Zn/Al/Mn<Cu/Zn/Al/La<Cu/Zn/Al/Ce<Cu/Zn/Al/Zr<Cu/Zn/Al/Y. The similar trend can be observed for the total number of basic sites, while the Zr-modified Cu/Zn/Al catalyst exhibits the highest density and proportion of strongly basic sites. It is also found that the CO2 conversion depends on the exposed Cu surface area and the CH3OH selectivity increases linearly with the increase of proportion of strongly basic sites to the total basic sites. The introduction of Mn, La, Ce, Zr and Y favors the production of methanol and the Y- and Zr-modified Cu/Zn/Al catalysts exhibit the highest CO2 conversion and CH3OH selectivity, respectively.

Nanosized CuO and ZnO Catalyst Supported on Titanium Chip for Conversion of Carbon Dioxide to Methyl Alcohol

In order to reutilize spent metallic titanium chips (TC) as catalyst support or photocatalytic materials, the surface of the TC was modified by thermal treatment under air atmosphere. TC-supported nanosized CuO and ZnO catalysts were prepared by impregnation (IMP) and co-precipitation (CP) method, respectively. The catalytic activity for CO2 hydrogenation to CH3OH was investigated using a flow-typed reactor under various reaction pressures. The crystals of CuO and ZnO was well formed on TC. CO2 conversion, CH3OH selectivity, and CH3OH yield were obtained as a function of time on stream over CuO-ZnO/TC catalysts. Conversion of CO2 to CH3OH over CuO-ZnO/TC catalyst by CP method and CuO/ZnO/TC catalyst by IMP method were ca. 16% and ca. 12%, respectively. Conversion of CO2 over CuO-ZnO/TC catalyst by CP method was increased with increasing reaction temperature in the range of 15-30 atm. Maximum selectivity and yield to CH3OH over CuO-ZnO/TC at 250 degrees C were ca. 90% at 20 atm and ca. 18.2% at 30 atm, respectively.

Influence of fluorine on the performance of fluorine-modified Cu/Zn/Al catalysts for CO2 hydrogenation to methanol

Fluorine-modified Cu/Zn/Al catalyst was prepared by calcination of the fluorine-containing Cu/Zn/Al hydrotalcite-like precursor and tested for CO2 hydrogenation to methanol. The introduction of fluorine into Cu/Zn/Al catalyst led to lower CO2 conversion mainly due to the decrease of the exposed copper surface area. However, the turnover frequency increased remarkably owing to the higher amount of easily reducible CuO. In addition, the CH3OH selectivity was greatly improved by the remarkable increase of the proportion of strongly basic sites to the total basic sites. As a result, the presence of fluorine in Cu/Zn/Al catalyst was favorable for CO2 hydrogenation to methanol, and the CH3OH yield for the fluorine-modified Cu/Zn/Al catalyst was higher than that for the fluorine-free Cu/Zn/Al catalyst.

Influence of Zr on the performance of Cu/Zn/Al/Zr catalysts via hydrotalcite-like precursors for CO2 hydrogenation to methanol

A series of Cu/Zn/Al/Zr hydrotalcite-like precursors with Zr4+:(Al3++Zr4+) from 0 to 0.7 were synthesized by a co-precipitation method. X-ray diffraction and thermogravimetric measurements demonstrated that the yield of the hydrotalcite-like phase decreases with increased Zr content. The Cu/Zn/Al/Zr mixed oxides were then obtained by calcination of the hydrotalcite-like precursors and tested for methanol synthesis from CO2 hydrogenation. With increased Zr4+:(Al3++Zr4+) atomic ratio, the exposed Cu surface area and dispersion of Cu first increase until Zr4+:(Al3++Zr4+)=0.3 and then decrease. However, the total number of basic sites on catalysts increases continuously. It is also found that the CO2 conversion is related to the exposed Cu surface area and the dispersion of Cu, while the CH3OH selectivity is related to the distribution of basic sites on the catalyst surface. The incorporation of a suitable amount of Zr is beneficial for the production of methanol, and the best catalytic performance is obtained when the Zr4+:(Al3++Zr4+) atomic ratio is 0.3.

CO2 capture via catalytic hydrogenation to methanol: Thermodynamic limit vs. ‘kinetic limit’

The production of methanol via the catalytic hydrogenation of carbon oxides was simulated in a reacting system that included the recycling of noncondensable gases (H2, CO2 and CO) to evaluate the CO2 capture capability of the process. As a first step, the asymptotic responses of the system ‘operating in thermodynamic equilibrium’ (i.e., overall recoveries of CO2 and H2, CH3OH selectivity and productivity) were analyzed for various industrial conditions of pressure (3–5MPa), temperature (508–538K), feed composition (H2/CO2=1.5/1 to 4/1) and mole recycle ratio (R) with respect to the molar feed flow rate. Then the performance of two catalysts (a novel one, Pd–Ga2O3/SiO2 and a commercial CuO/ZnO/Al2O3 type) in an ideal isothermal, isobaric, pseudohomogeneous fixed-bed reactor was studied for a broad range of W/FCO2 ratios.It was found that, whereas the ‘reactor in equilibrium’ would allow up to 100% CO2 capture, the capture values upon using these catalysts were significantly lower. Nevertheless, such recoveries always increased whenever R was raised, which implies that catalyst development efforts in this field should prioritize achievement of the highest catalytic activity (i.e., specific productivity) rather than attempt catalyst selectivity improvements.

A Highly Hydrophobic Metal−Organic Framework Zn(BDC)(TED)0.5 for Adsorption and Separation of CH3OH/H2O and CO2/CH4: An Integrated Experimental and Simulation Study

The adsorption and separation of CH3OH/H2O and CO2/CH4 in Zn(BDC)(TED)0.5 (BDC = benzenedicarboxylate, TED = triethylenediamine) are investigated by integrating experiment and simulation. Zn(BDC)(TED)0.5 is a highly hydrophobic metal−organic framework (MOF) with interlacing channels. The simulated isotherms of CH3OH and H2O are in fairly good agreement with experimental results. While H2O adsorption in Zn(BDC)(TED)0.5 is vanishingly small, CH3OH shows a much stronger adsorption. The selectivity of CH3OH over H2O is approximately 20 at low pressures and the selectivity decreases with increasing pressure. From the density distributions and structural analysis, it is found that CH3OH interacts strongly with the metal oxides, particularly at low pressures. The isotherms of CO2 and CH4 from simulation match well with experimental data. As a nonpolar molecule, CO2 exhibits different favorable sites from polar CH3OH. At low pressures, CO2 is located preferentially near the BDC linkers. As pressure increases, CO2...

Characterization and DFT Research of Nd/TiO2: Photocatalyst for Synthesis of Methanol from CO2 and H2O

Abstract Nd3+–doped TiO2 synthesized via the sol-gel method, was used as catalyst for photoreduction of carbon dioxide into methanol in an aqueous solution under UV irradiation. The catalysts were characterized by XRD, IR, UV-vis etc. The maximum photocatalytic activity corresponds to the 0.2 wt.% Nd3+–doped TiO2 nanopowders. In that case, the methanol yield is 184.8μmol/g by 8h UV irradiation, indicating that the Nd/TiO2 can obviously enhance the efficiency of photocatalytic reduction comparing to pure TiO2. Furthermore, the adsorption properties of Nd atom on the regular (110) surface of rutile and (101) surface of anatase were studied by density functional calculations under the B3LYP level. H2O molecule catches the photo-induced hole in the reaction system forming H2O+ which dissociates further into H+ and OH radical on the catalyst surface. The transition state was found by DFT calculation, and the amount of the OH radicals has effects on the selectivity of CH3OH.

Enhancement of methanol selectivity in the products of direct selective oxidation of methane in CH 4-O 2-NO with Cu-ZnO/SiO 2

Enhancement of methanol selectivity in the products of the direct selective oxidation of methane with CH 4-O 2-NO in a gas-phase reaction was examined using a Cu-ZnO/SiO 2 catalyst. Two types of Cu-ZnO/SiO 2 catalysts were prepared with different compositions: 3:7:90 (denoted as CZS-1) and 5:5:90 (CZS-2) as the weight percent ratios of CuO:ZnO:SiO 2. Both CH 3OH and CH 2O were observed as C 1-oxygenates at 550 °C in the gas-phase selective oxidation of CH 4 in CH 4-O 2-NO without a catalyst, but then only CH 3OH was observed in the presence of the CZS-1, in addition to the direct gas-phase selective oxidation of methane. The catalyst temperature was 250 °C and the reaction pressure was 0.4 MPa. CH 3OH, CO and CO 2 selectivities increased and CH 2O selectivity decreased in the presence of the Cu-ZnO/SiO 2, in comparison to the values in the absence of the catalyst. We, therefore, suggested that three reactions: i.e. the hydrogenation reaction of CH 2O, the dissociation reaction of CH 2O, and the WGSR, progressed simultaneously on the Cu-ZnO/SiO 2 catalyst in CH 4-O 2-NO. Since the selectivity of CH 3OH did not vary during the variation of reaction temperatures from 150 °C up to 350 °C over the Cu-ZnO/SiO 2 catalyst, we assumed that SiO 2 was a favorable support to enhance the selectivity of CH 3OH in a wider catalyst temperature region.

Simulation of CO 2 hydrogenation with CH 3OH removal in a zeolite membrane reactor

A thermodynamic analysis of the CO 2 hydrogenation to methanol where competitive reactions take place is presented for a membrane reactor (MR) where methanol was selectively removed. A non-isothermal mathematical model was written to simulate a micro-porous MR. Zeolite membranes with different values of the CH 3OH and H 2O permeances were considered in the MR modelling. The effect of temperature, pressure and species permeation on the conversion, selectivity and yield was analysed. A higher CO 2 conversion and CH 3OH selectivity can be reached by the use of an MR. An increased CH 3OH yield allows to reduce the consumption of reactant and also to operate at lower pressures and higher temperatures, a fact, which favours the kinetics reducing the residence time and the reactor volume. The MR with the highest CH 3OH/H 2O permeance ratio resulted in better selectivity and yield of CH 3OH with respect to the other MR characterised by a higher conversion.

Selective oxidation of methane in CH 4–O 2–NO 2 over MoO 3

Selective oxidation of methane in CH 4–O 2–NO 2 was examined using MoO 3 catalyst at atmospheric pressure. The selective oxidation was enhanced with addition of NO 2 to the reaction system of CH 4 and O 2, in analogy with the gas-phase reaction. The initiation reaction was assured to take place between CH 4 and NO 2. The presence of MoO 3 catalyst increased CH 2O selectivity and decreased CH 3OH selectivity, compared with those for the gas-phase reaction in CH 4–O 2–NO 2. Based on variations in reaction of selectivities at several reaction conditions, it could be explained/concluded that formaldehyde was a main product on the MoO 3 catalyst and methanol was formed through gas-phase reactions.

Effects of lowering reaction temperatures in the direct selective oxidation of CH 4–O 2–NO 2–CH 2O

The lowering effects of reaction temperatures on both methane activation and C 1 oxygenates selectivity have been examined for the selective oxidation of methane in the gas-phase reaction of CH 4–O 2–NO 2 with CH 2O addition (CH 2O add) in a feed gas. Formaldehyde addition in the feed gas was effective to enhance methane activation. Reaction temperature was decreased ca. 50 K at 5% level of CH 4 conversion by (CH 2O add) to 1.1% level in the feed gas of CH 4–O 2–NO 2. This decrease was explained by the lowering effects of activation energy for hydrogen abstraction reaction from methane. Formaldehyde selectivity decreased at the same reaction temperature as the CH 2O add concentration in the feed gas was increased. This decrease was explained by the increase of decomposition reaction between produced CH 2O and OH which was produced through CH 2O related reactions. The enhancement of CH 3OH selectivity by the addition of CH 2O in a lower temperature region was observed. It was explained by newly appeared CH 3OH formation route, which was derived from the CH 2O add in the feed gas.

The effects of reaction pressures on the production of methanol through the selective oxidation of methane in CH 4–O 2–NO x ( x=1 or 2)

The effects of reaction pressures on the selective formation of methanol in a gas phase selective oxidation of CH 4 with NO x ( x=1 or 2) were examined. Methane conversion was enhanced by the addition of a small amount of NO x (0.125–1.50% ) in a feed gas and also enhanced by raising reaction pressures. The transition barrier of hydrogen abstraction from methane with NO 2, i.e. CH 4+NO 2→CH 3 +H–NO 2 was lower than that with O 2, and the number of these reactions between CH 4 and NO 2 in a higher pressure reactor was increased. A lower reaction temperature was favorable to enhance the selectivity of CH 3OH, and a shorter mean free path in a higher-pressure reactor simultaneously increased the subsequential oxidation of CH 3OH. The optimum pressure for the production of methanol at 4% conversion of CH 4 was 1.0 MPa for the selective oxidation of methane with 0.50% NO.

Reactivity and π-facial selectivity of nucleophile addition to the radical cations of 7-benzhydrylidenenorbornene derivatives

For correlating a homoconjugation structure of a radical cation to its reactivity with a nucleophile, the reactivity and π-facial selectivity of CH 3OH and H 2O addition to the radical cations of 7-benzhydrylidenenorbornene derivatives generated by photoinduced electron transfer reactions were investigated.

SELECTIVITIES OF GROUP VIII METALS FOR THE HYDROGENATION OF FORMALDEHYDE AND THE EFFECT OF SUPPORT AND PROMOTER

Abstract The reaction of HCHO over group VIII metals was studied. The main products obtained with powder catalysts were CO and CH3OH, while CH4 was formed at higher temperatures. The CH3OH selectivity of the powder catalysts correlated well with the heat of formation of oxide. Although the SiO2 support did not affect the CH3OH selectivity of the metal, ZnO and Cs2O improved it remarkably. Cu–Zn–Al catalysts are quite active for CH3OH formation.