Formation Of Dimethyl Ether Research Articles

Zeolites as Solid Solvents: Explaining the Chloromethane Hydrolysis over Metal-Exchanged Zeolite Y by DFT Calculations.

We report a theoretical DFT study of the reaction pathways for chloromethane hydrolysis over metal-exchanged zeolites (Li+, Na+, K+, and Mg2+). A cluster of 78 T atoms (T referring to Si or Al atoms), comprising the zeolite Y super cavity coupled with the sodalite cage and three hexagonal prism units (Si(78-x)Al x O129H54; x = 1 or 2), was used in the calculations. The study was carried out using the ONIOM method. The high layer was computed at M062X/6-31++G(d,p), whereas the low layer was computed at the PM6 level of theory. The energy profile was obtained by single-point calculations at the M062X/6-31++G(d,p) for the entire structure. The first step studied was the adsorption of chloromethane on the zeolite, which involves an ion-dipole interaction between the metal cation and the chlorine atom. Then, two mechanistic pathways were investigated: one via formation of an adsorbed methoxide and the other involving a direct, one-step, nucleophilic attack of the water molecule to the adsorbed chloromethane. In all systems studied, the direct mechanism showed a lower energy of activation than the route involving the methoxide intermediate. The same behavior was also observed for chloromethane methanolysis to afford dimethyl ether on the metal-exchanged zeolites. The theoretical results are in agreement with the experiments of chloromethane hydrolysis over metal-exchanged zeolite Y, explaining the formation of dimethyl ether upon chloromethane methanolysis on zeolites of low or no acidity. The transition state for the direct route resembles a SN2 process assisted by the surface, reinforcing the concept of zeolites as solid solvents, providing a polar nanoenvironment that favors and assists the formation of ionic transition states and intermediates.

Structure and reactivity of surface vanadia sites in bi-layered supported VOx/AlOx/SiO2 catalysts via solid-state NMR, first-principles calculations, and catalytic studies

By combining multinuclear 1H, 29Si, 27Al and 51V solid-state NMR experimental measurements with reactivity and selectivity data, as well as first-principles calculations, for ternary bi-layered supported VOx/Al2O3/SiO2 catalysts, the structure of the dehydrated surface vanadia species was determined for each combination of supported VOx and AlOx active components. The specific structure of the surface vanadia sites in the ternary bi-layered supported VOx/Al2O3/SiO2 catalyst system have been investigated for the first time.The following vanadia sites are proposed based on the current findings:At low vanadia content, surface VO(OH)(OSi)2 sites form on the alumina-free surface of the SiO2 support in the bi-layered supported VOx/Al2O3/SiO2 catalyst system. In addition, two types of VO(OSi)3 surface species are likely present in this system. On small alumina clusters, weakly bonded surface VO(OH)(OAl)2 sites also form, along with the sites containing mixed Si/Al pods VO(OH)(OAl)(OSi). As the size of alumina clusters increases, strongly bonded VO(OAl)3 centers form, alongside the surface sites containing mixed pods VO(OAl)2(OSi) and VO(OAl)(OSi)2. The content of these sites increases with the loading of vanadia. Comparing supported VOx/SiO2, VOx/Al2O3, and bi-layered VOx/Al2O3/SiO2 catalyst systems revealed differences in catalytic activity due to the presence of new sites with different pods, with OH groups as well as the influence of Al-O-Si bonds on the electronic structure of surface vanadia sites on the alumina clusters. During the formation of dimethyl ether (DME), the turnover frequency (TOFDME) of the catalysts decreases with increasing domain size of the alumina clusters on SiO2. Addition of surface VOx sites, however, slightly decreases the TOFDME with the higher vanadia content weakening the activity of the alumina clusters. When surface VOx exists predominantly as V/Al1 and V/Al2, TOFredox depend on the vanadia content with lower vanadia content resulting in higher the TOFredox values. The 51V NMR spectra show that this decrease in redox TOF value correlates with the appearance of vanadia sites associated with silica pods. The activity of the catalysts was tested in methanol conversion reactions.

Non‐Oxidative Conversion of Methanol to Dimethyl Ether, Methyl Formate and Dimethoxymethane over Cu/Hβ Catalyst: Tailoring Product Selectivity

AbstractHerein, we present the production of either dimethyl ether (DME), methyl formate (MF) or dimethoxymethane (DMM), representing pivotal molecules for the green transformation of fuels and chemical industry, by the non‐oxidative gas‐phase conversion of methanol under the same reaction conditions. The product selectivity is optimized by tailoring the acidic and dehydrogenative sites of the bifunctional Cu/Hβ catalyst system by varying the SiO2/Al2O3 ratio of the Hβ zeolite (25 and 520) and the Cu loading (0.5 and 20 wt %). At 240 °C, >99 % (DME), 74.5 % (MF), and 77.3 % (DMM) selectivity is achieved with the respective catalysts 0.5 %Cu/Hβ(25), 20 %Cu/Hβ(520), and 0.5 %Cu/Hβ(520). High acidic site concentration catalyzes DME formation, while the presence of Cu+ species is crucial for DMM formation, and Cu0 species mainly catalyze MF formation. A highly dynamic reaction behaviour is observed, when the dehydrogenative functionality is dominant (i. e., in the production of MF or DMM), presumably due to the dynamic nature of the Cu oxidation state, which is in turn influenced by possible by‐products (H2 and H2O). While the catalytic activity in DME synthesis over 0.5 %Cu/Hβ(25) is remarkably stable over 1500 min TOS, the activity in MF and DMM production over 20 %Cu/Hβ(520) and 0.5 %Cu/Hβ(520), respectively, can be successfully regenerated.

Multilevel quantum mechanical calculations show the role of promoter molecules in the dehydration of methanol to dimethyl ether in H-ZSM-5.

Methyl carboxylate esters promote the formation of dimethyl ether (DME) from the dehydration of methanol in H-ZSM-5 zeolite. We employ a multilevel quantum method to explore the possible associative and dissociative mechanisms in the presence, and absence, of six methyl ester promoters. This hybrid method combines density functional theory, with dispersion corrections (DFT-D3), for the full periodic system, with second-order Møller-Plesset perturbation theory (MP2) for small clusters representing the reaction site, and coupled cluster with single, double, and perturbative triple substitution (CCSD(T)) for the reacting molecules. The calculated adsorption enthalpy of methanol, and reaction enthalpies of the dehydration of methanol to DME within H-ZSM-5, agree with experiment to within chemical accuracy (∼4 kJ mol-1). For the promoters, a reaction pathway via an associative mechanism gives lower overall reaction enthalpies and barriers compared to the reaction with methanol only. Each stage of this mechanism is explored and related to experimental data. We provide evidence that suggests the promoter's adsorption to the Brønsted acid site is the most important factor dictating its efficiency.

Nanostructured sustainable carbon derived from biomass as catalyst support for alumina in catalytic methanol conversion to DME as hydrogen carrier

A novel series of nanostructured catalysts composed of Al2O3 supported on a phosphorous (P) modified mesoporous carbon (ACP) derived from orange peel residues was formed. The formed, 1−7% (w/w) alumina/ACP, catalysts were investigated for conversion of methanol to dimethyl ether (DME) as a promising hydrogen carrier. The catalysts were characterized with a group of standard characterization techniques. Increasing of alumina loading caused remarkable structural and textural changes. Thus, new bands due to Al–O–P was detected by ATR−FTIR, which was confirmed by XPS as due to surface AlPO4 species. However, no crystalline Al2O3 and/or AlPO4 nanoparticles were detected by XRD or HRTEM. Meanwhile, the mesoporous surface texture was preserved. The loading of alumina led to increasing of Brønsted acidic sites population. The catalyst exhibited high conversion of methanol and complete selectivity for DME at low, DME formation rate of 17.88 and 19.85 mmol g−1 h−1 at 300 and 350 °C, respectively. The catalyst efficiency is among the most efficient traditional and recently reported catalysts. Thus, the work showed successful biomass valorization into efficient, selective, low price catalysts that facilitate hydrogen storage via conversion of methanol to DME. This conversion, which is advantageous in transportation and distribution as H2 carrier, will in fact support and advance the UN's sustainable development goals.

Atomically Thick Oxide Overcoating Stimulates Low-Temperature Reactive Metal-Support Interactions for Enhanced Catalysis.

Reactive metal-support interactions (RMSIs) induce the formation of bimetallic alloys and offer an effective way to tune the electronic and geometric properties of metal sites for advanced catalysis. However, RMSIs often require high-temperature reductions (>500 °C), which significantly limits the tuning of bimetallic compositional varieties. Here, we report that an atomically thick Ga2O3 coating of Pd nanoparticles enables the initiation of RMSIs at a much lower temperature of ∼250 °C. State-of-the-art microscopic and in situ spectroscopic studies disclose that low-temperature RMSIs initiate the formation of rarely reported Ga-rich PdGa alloy phases, distinct from the Pd2Ga phase formed in traditional Pd/Ga2O3 catalysts after high-temperature reduction. In the CO2 hydrogenation reaction, the Ga-rich alloy phases impressively boost the formation of methanol and dimethyl ether ∼5 times higher than that of Pd/Ga2O3. In situ infrared spectroscopy reveals that the Ga-rich phases greatly favor formate formation as well as its subsequent hydrogenation, thus leading to high productivity.

Effectiveness of the 3D-printing procedure in the synthesis of hybrid catalysts for the direct hydrogenation of CO2 into dimethyl ether

This work highlights the effectiveness of an unconventional synthesis of hybrid systems for the direct hydrogenation of carbon dioxide into dimethyl ether (DME), based on micro-extrusion of a ink-like catalytic paste by a robocasting procedure. Due to the possibility to exert a fine control over the structure, surface and geometric architecture, the adopted printing technique really ensures a superior management of heat and mass constraints in respect of the conventional powdered catalysts, the catalyst functionality resulting to be tightly dependent on the cooperation between metal-oxide and acidic phase. Additionally, the accessibility both of the CO2 activation and methanol (MeOH) dehydration sites over the hybrid micro-extruded catalyst most importantly affects the catalytic performance, as suggested by the values of turnover frequency of CO2 conversion and DME formation pointing out the need for a favorable exposure of chemisorption sites of different nature to enhance the specific reactivity.

Kinetic and Spectroscopic Studies of Methyl Ester Promoted Methanol Dehydration to Dimethyl Ether on ZSM-5 Zeolite

Methyl carboxylate esters have been shown to be potent promoters of low-temperature methanol dehydration to dimethyl ether (DME) using various zeolite catalysts. In the present work, catalytic kinetic studies, in-situ Fourier-transform infrared spectroscopy (FT-IR) and solid-state nuclear magnetic resonance spectroscopy (NMR) techniques were used to elucidate the promotional mechanism of methyl carboxylate esters on methanol dehydration to DME, using the medium pore zeolite H-ZSM-5 (MFI) as the catalyst. Kinetic studies were performed using the very potent methyl n-hexanoate promoter. The DME yield was dependent on both the methanol and methyl n-hexanoate partial pressures across the temperature ranges used in this study (110 to 130 °C). This is consistent with the promoted reaction being a bimolecular reaction between methanol and ester species adsorbed at the catalyst active sites, via an SN2 type reaction, as previously postulated. The in-situ FT-IR studies reveal that the Brønsted acid (BA) sites on H-ZSM-5 were very rapidly titrated by ester carbonyl group adsorption and bonded more strongly with esters than with methanol. Upon methanol addition, an even lower DME formation temperature (30 °C) was observed with methyl n-hexanoate pretreated H-ZSM-5 samples in the in-situ NMR studies, further confirming the strong promotion of this methyl ester on methanol dehydration to DME. The adsorption and reactivity of different methyl esters on H-ZSM-5 indicates that while methyl formate more easily dissociates into a surface methoxy species, [Si(OMe)Al], and carboxylic acid, it is a less potent promoter than alkyl-chain-containing methyl esters in methanol dehydration to DME, which in turn did not show this dissociative behavior in the low-temperature NMR studies. This indicates that methyl alkyl carboxylates do not need to be dissociated to a surface methoxy species to promote the methanol dehydration reaction and that a bimolecular associative mechanism plays an important role in promoting DME formation.

Direct conversion of water to hydrogen peroxide on single electrode towards partial oxidation of propylene

We report an approach of direct production of H2O2 from water by applying altering potential in the electrocatalysis. By switching potentials periodically between positive to negative, oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) occurs sequentially on a single electrode loaded catalysts, which leads to the reduction of the newly-formed OER active species, forming H2O2 directly. The H2O2 production is dependent on the time and potentials of OER and ORR, which is optimized in this study. Besides, a waiting time is set after each period to let H2O2 diffusion from the catalyst surface. Different catalysts are employed to test the feasibility of this approach, including glassy carbon, graphene oxide, nickel particles, nickel foam, and palladium particles. All these catalysts result in the production of H2O2 at various reaction rates. Ni offers the highest H2O2 productivity. With the prolonging of the reaction time, the decomposition of H2O2 occurs on the surface of Ni catalysts, which is inhibited by the addition of Zn into the catalysts. The in-situ generated H2O2 is used for partial oxidation of propylene by passing propylene into the porous electrode during the reaction, which lead to the formation of dimethyl ether and adipic acid. This study shows a new route of the direct synthesis and utilization of H2O2 for the generation of valuable chemicals.

Dimethyl ether (DME) synthesis from CO2 and H2 through ethanol-assisted methanol synthesis and methanol dehydration

Two steps of dimethyl ether (DME) synthesis from CO2 and H2 in a batch reactor were studied, including CO2 hydrogenation to methanol through ethanol-assisted method and methanol dehydration to DME. Additions of 10 wt% ZrO2, Al2O3 and ZrO2–Al2O3 into Cu/ZnO were investigated in low-temperature methanol synthesis using ethanol as catalytic solvent. Suitable zeolite (ZSM-5 and ferrierite) for methanol dehydration was also determined. Ethanol-assisted method offered high methanol yield and Cu/ZnO/ZrO2 catalyst provided the highest CO2 conversion (82.1%) and methanol yield (60.8%) at 150 °C and 50 bar since ZrO2 decreased CuO crystallite sizes and increased surface areas of the catalyst. For methanol dehydration to DME, zeolite's strong acidity related to DME formation. The Cu/ZnO/ZrO2 - Ferrierite provided the highest DME productivity at 0.44 mmolDME/gcat. In addition, DME synthesis from CO2 and H2 through ethanol-assisted methanol synthesis and methanol dehydration can be a potential method to simultaneously produce DME and ethylene. Under the operating conditions, ethylene was produced as a valued by-product of 5.65 mmolEthylene/gcat from dehydration of ethanol. In this study, rather high methanol yield was obtained from ethanol-assisted method. However, DME yield can be further improved by increasing synthesis temperature.

Effect of Support and Pd Cluster Size on Catalytic Methane Partial Oxidation to Dimethyl Ether Using a NO/O2Shuttle

The partial oxidation of methane to dimethyl ether (DME) was studied on palladium supported on SiO2, SiO2-ZrO2, and ZrO2 at 225–375 °C and 0.1 MPa using either O2 or a mixture of NO and O2 as the oxidants. The NO + O2 mixture was more reactive than the O2 toward methane, probably due to the formation of active surface nitrate species. The formation of DME on the catalysts was influenced by the support, with the Pd/ZrO2 catalyst producing DME and the Pd/SiO2 catalyst producing only CO2, irrespective of the oxidant used. The Pd/SiZrO2 catalyst formed DME only when O2 alone was used as the oxidant. For the reaction with NO + O2, in situ Fourier transform infrared (FTIR) measurements showed that the partial oxidation activity on Pd/ZrO2 was related to its ability to form surface-bridged nitrate species, likely due to the presence of basic sites. However, an inhibitory effect of basicity on CH4 turnover frequency (TOF) was attributed to surface nitrate-induced structural modification deduced from X-ray absorption fine structure spectroscopy measurements. For the reaction with only O2, the formation of DME over Pd/ZrO2 and Pd/SiZrO2 was attributed to the reported ability of ZrO2 to retain methoxy intermediates. Furthermore, a weak structural effect on the TOF observed with O2 was attributed to competing effects of decreasing activity for C-H activation and increasing resistance to Pd oxidation with increasing particle size.

Interaction of Methanol over CsCl- and KCl-Doped η-Alumina and the Attenuation of Dimethyl Ether Formation

As part of a program to investigate aspects of surface chemistry relevant to methyl chloride synthesis catalysis, the interaction of methanol with η-alumina doped with either CsCl or KCl in the range 0.01–1.0 mmol g(cat)–1 is investigated by a combination of diffuse reflectance infrared Fourier transform spectroscopy and temperature-programed desorption (TPD). Infrared spectra (IR) recorded at 293 K show that increasing the concentration of the group 1 metal chloride progressively decreases the surface concentration of associatively chemisorbed methanol and changes the environment in which the adsorbed methanol resides. For CsCl concentrations of ≥0.6 mmol g(cat)–1, chemisorbed methoxy species dominate the IR spectrum, while TPD studies show that the amount of methanol adsorbed onto the surface, and subsequently desorbed unchanged, changes relatively little. In the TPD experiments, some of the adsorbed methanol reacts to give dimethyl ether (DME) which then desorbs; for dopant concentrations of 1.0 mmol g(cat)–1, DME formation is suppressed to below the limit of detection. Unexpectedly, the presence of formate species generated at 293 K is also observed spectroscopically, characterized by a νasym(COO) mode which exhibits a hypsochromic shift relative to potassium formate; surface concentrations of formate are higher at higher loadings of group 1 metal chloride. Temperature-programed IR spectroscopy shows that the room-temperature formate species desorbs, decomposes, or migrates on warming to 653 K. Thermal ramping of the methanol-saturated surface also results in formate production but one that exhibits an IR profile in agreement with earlier observations and literature values. Increasing the concentrations of the group 1 metal chloride progressively decreases the presence of the thermally induced formate moiety. The study not only reinforces the concept of group 1 metal chloride additives progressively rendering ineffective those Lewis acid sites present at the η-alumina surface which convey discrete reaction characteristics [e.g., (i) dimerization of methanol to form DME and (ii) an activated methoxy → formate transition] but also suggests the generation of reactive sites not present in the undoped alumina.

Lignin as a Bio-Sourced Secondary Template for ZSM-5 Zeolite Synthesis

The aim of this study was to investigate the effect of the addition of lignin as a sacrificial agent in ZSM-5 zeolite synthesis. Peculiar growths of ZSM-5 crystals leading to various textural properties were observed. Hence, the behavior in acid-catalyzed conversion of methanol into hydrocarbons (MTH) shifted from high selectivity toward olefins (>55%) to the sole formation of dimethyl ether (DME). Lignin acted as a bio-sourced secondary template (BSST), impacting the zeolite crystals’ shape and, thus, their physicochemical properties.

Quantum Mechanical Simulations of the Radical–Radical Chemistry on Icy Surfaces

Abstract The formation of the interstellar complex organic molecules (iCOMs) is a hot topic in astrochemistry. One of the main paradigms trying to reproduce the observations postulates that iCOMs are formed on the ice mantles covering the interstellar dust grains as a result of radical–radical coupling reactions. We investigate iCOM formation on the icy surfaces by means of computational quantum mechanical methods. In particular, we study the coupling and direct hydrogen abstraction reactions involving the CH3 + X systems (X = NH2, CH3, HCO, CH3O, CH2OH) and HCO + Y (Y = HCO, CH3O, CH2OH), plus the CH2OH + CH2OH and CH3O + CH3O systems. We computed the activation energy barriers of these reactions, as well as the binding energies of all the studied radicals, by means of density functional theory calculations on two ice water models, made of 33 and 18 water molecules. Then, we estimated the efficiency of each reaction using the reaction activation, desorption, and diffusion energies and derived kinetics with the Eyring equations. We find that radical–radical chemistry on surfaces is not as straightforward as usually assumed. In some cases, direct H-abstraction reactions can compete with radical–radical couplings, while in others they may contain large activation energies. Specifically, we found that (i) ethane, methylamine, and ethylene glycol are the only possible products of the relevant radical–radical reactions; (ii) glyoxal, methyl formate, glycolaldehyde, formamide, dimethyl ether, and ethanol formation is likely in competition with the respective H-abstraction products; and (iii) acetaldehyde and dimethyl peroxide do not seem to be likely grain-surface products.

Quantifying Effects of Active Site Proximity on Rates of Methanol Dehydration to Dimethyl Ether over Chabazite Zeolites through Microkinetic Modeling.

Control of the spatial proximity of Brønsted acid sites within the zeolite framework can result in materials with properties that are distinct from materials synthesized through conventional crystallization methods or available from commercial sources. Recent experimental evidence has shown that turnover rates of different acid-catalyzed reactions increase with the fraction of proximal sites in chabazite (CHA) zeolites. The catalytic conversion of oxygenates is an important research area, and the dehydration of methanol to dimethyl ether (DME) is a well-studied reaction as part of methanol-to-olefin chemistry catalyzed by solid acids. Published experimental data have shown that DME formation rates (per acid site) increase systematically with the fraction of proximal acid sites in the six-membered ring of CHA. Here, we probe the effect of acid site proximity in CHA on methanol dehydration rates using electronic structure calculations and microkinetic modeling to identify the primary causes of this chemistry and their relationship to the local structure of the catalyst at the nanoscale. We report a density functional theory-parametrized microkinetic model of methanol dehydration to DME, catalyzed by acidic CHA zeolite with direct comparison to experimental data. Effects of proximal acid sites on reaction rates were captured quantitatively for a range of operating conditions and catalyst compositions, with a focus on total paired acid site concentration and reactant clustering to form higher nuclearity complexes. Next-nearest neighbor paired acid sites were identified as promoting the formation of methanol trimer clusters rather than the inhibiting tetramer or pentamer clusters, resulting in large increases in the rate for DME production due to the lower energy barriers present in the concerted methanol trimer reaction pathway. The model framework developed in this study can be extended to other zeolite materials and reaction chemistries toward the goal of rational design and development of next-generation catalytic materials and chemical processes.

Radiative Association between Neutral Radicals in the Interstellar Medium: CH3 + CH3O

Abstract Uncertainties in the production mechanisms of interstellar complex organic molecules call for a precise investigation of gas-phase synthetic routes for these molecules, especially at low temperatures. Here, we report a study of the gas-phase formation of dimethyl ether from the neutral radicals methyl and methoxy via the process of radiative association. This process may be important to synthesize dimethyl ether and species such as methyl formate, for which dimethyl ether is a precursor. The reaction is found to be rapid by the standards of radiative association, especially at 10 K, where its rate coefficient is calculated by two different methods to be 3 × 10−11 or 2 × 10−10 cm3 s−1; the lower rate is calculated with a more precise theory and is likely more accurate. Insertion of this reaction into the Nautilus network is found not to explain fully the abundance of dimethyl ether in cold and prestellar cores, especially in those cores with the highest dimethyl ether abundances.

Turning CO2 into di-methyl ether (DME) using Pd based catalysts – Role of Ca in tuning the activity and selectivity

Herein, we report high-performance Pd and Ca-promoted Pd nanoparticles (NPs) (~2–6 nm) over mesoporous CeO2 with dual functionality of converting CO2 to methanol and its dehydration to di-methyl ether (DME) in a single catalyst bed prepared by a single-pot sol–gel chelating (SGC) method. Moreover, Ca promotion (0.5wt. %, optimized value) greatly improved the catalytic performance (XCO2: 30.5 %, SDME: 70.5 % and space time yield (STYDME): 5276 mmol/kgcat.hr at 325 °C and 20 Bar) by increasing Pd0 content over CeO2 and tuned the redox properties of CeO2 as well as basicity/acidity of tested samples as evidenced by the characterization results. In situ diffuse reflectance infrared fourier transform spectroscopy (DRIFTS) provided insights of the formation of DME and CH4 with visible respective IR bands along with the identification of various transient surface species emerged over the catalyst surface at actual reaction conditions which led us to propose a reaction mechanism following a formate route to methanol and its subsequent dehydration to dimethyl ether.

Ni-MoOx bifunctional catalyst on SiO2 for vapor halide-free methanol carbonylation: Insight into synergistic catalysis between Ni and MoOx

A promising Ni-MoOx bifunctional catalyst for halide-free methanol carbonylation is developed by H2-reduction of NiO-MoO3/SiO2 obtained via facile impregnation method. Catalyst performance is strongly dependent on the calcination/reduction temperature. Over the preferable NiMo-350-600/SiO2 catalyst obtained by calcining at 350 °C and subsequently reducing at 600 °C, a methanol conversion of 4.2 % and acetyls space-time yield of 1.37 mol kgcat−1 h−1 are achieved with 22.1 % selectivity to acetyls at 290 °C and 3 MPa. Co-existence of Ni0 and MoOx (especially MoO2) markedly decreases formation of dimethyl ether (DME) and reversely increases acetyls formation, in nature, due to the catalyst acidity modulation and the partial electron transfer from Ni0 to MoOx that tunes the CO adsorption strength on Ni0 sites. MoO3 and NiMoO4 are both favorable for formation of acetyls and DME whereas the latter mainly accounts for DME formation. MoNi4 alone favors methyl formate formation while together with MoO2 enhancing DME production.

Investigation of alkaline complexant on ethanol synthesis from syngas over slurry CuZnAlOOH catalyst

A series of alkaline complexants promoted slurry CuZnAlOOH catalysts were prepared by a complete liquid-phase method. These catalysts were applied in a slurry bed reactor to selectively convert syngas into ethanol and higher alcohols (HAs). Herein, we showed that the addition of alkaline complexant remarkably enhanced both CO conversion and selectivity toward to ethanol and HAs in terms of ternary CuZnAlOOH catalyst. Besides, the formation of dimethyl ether (DME) was significantly suppressed. Interestingly, different from the traditional alkalis modified copper-based catalysts, these catalysts promoted by alkaline complexants mainly increased selectivity for ethanol, while not isobutanol. It also reduced the deactivation rate of the catalysts. These catalysts were comprehensively characterized by XRD, H2-TPR, NH3-TPD-MS, N2 adsorption, FT-IR, XPS and TEM techniques. It was found that the increase of ethanol selectivity was related to the decrease of catalyst surface acidity, while the decrease of surface Cu+/(Cu0+Cu+) was regarded to the main reason for the catalysts deactivation. This paper showed that the introduction of alkaline complexants into Cu-based catalysts exhibited the potentiality to improve the stability and the yield of ethanol in a slurry bed reactor.

Direct Synthesis of Dimethyl Ether from CO2: Recent Advances in Bifunctional/Hybrid Catalytic Systems

Dimethyl ether (DME) is a versatile raw material and an interesting alternative fuel that can be produced by the catalytic direct hydrogenation of CO2. Recently, this process has attracted the attention of the industry due to the environmental benefits of CO2 elimination from the atmosphere and its lower operating costs with respect to the classical, two-step synthesis of DME from syngas (CO + H2). However, due to kinetics and thermodynamic limits, the direct use of CO2 as raw material for DME production requires the development of more effective catalysts. In this context, the objective of this review is to present the latest progress achieved in the synthesis of bifunctional/hybrid catalytic systems for the CO2-to-DME process. For catalyst design, this process is challenging because it should combine metal and acid functionalities in the same catalyst, in a correct ratio and with controlled interaction. The metal catalyst is needed for the activation and transformation of the stable CO2 molecules into methanol, whereas the acid catalyst is needed to dehydrate the methanol into DME. Recent developments in the catalyst design have been discussed and analyzed in this review, presenting the different strategies employed for the preparation of novel bifunctional catalysts (physical/mechanical mixing) and hybrid catalysts (co-precipitation, impregnation, etc.) with improved efficiency toward DME formation. Finally, an outline of future prospects for the research and development of efficient bi-functional/hybrid catalytic systems will be presented.