Dehydrogenation Of Methanol Research Articles

Does Symmetry Control Photocatalytic Activity of Titania-Based Photocatalysts?

Decahedral anatase particles (DAPs) have been prepared by the gas-phase method, characterized, and analyzed for property-governed photocatalytic activity. It has been found that depending on the reaction systems, different properties control the photocatalytic activity, that is, the particle aspect ratio, the density of electron traps and the morphology seem to be responsible for the efficiency of water oxidation, methanol dehydrogenation and oxidative decomposition of acetic acid, respectively. For the discussion on the dependence of the photocatalytic activity on the morphology and/or the symmetry other titania-based photocatalysts have also been analyzed, that is, octahedral anatase particles (OAP), commercial titania P25, inverse opal titania with and without incorporated gold NPs in void spaces and plasmonic photocatalysts (titania with deposits of gold). It has been concluded that though the morphology governs photocatalytic activity, the symmetry (despite its importance in many cases) rather does not control the photocatalytic performance.

Single-atom catalyst for high-performance methanol oxidation

Single-atom catalysts have been widely investigated for several electrocatalytic reactions except electrochemical alcohol oxidation. Herein, we synthesize atomically dispersed platinum on ruthenium oxide (Pt1/RuO2) using a simple impregnation-adsorption method. We find that Pt1/RuO2 has good electrocatalytic activity towards methanol oxidation in an alkaline media with a mass activity that is 15.3-times higher than that of commercial Pt/C (6766 vs. 441 mA mg‒1Pt). In contrast, single atom Pt on carbon black is inert. Further, the mass activity of Pt1/RuO2 is superior to that of most Pt-based catalysts previously developed. Moreover, Pt1/RuO2 has a high tolerance towards CO poisoning, resulting in excellent catalytic stability. Ab initio simulations and experiments reveal that the presence of Pt‒O3f (3-fold coordinatively bonded O)‒Rucus (coordinatively unsaturated Ru) bonds with the undercoordinated bridging O in Pt1/RuO2 favors the electrochemical dehydrogenation of methanol with lower energy barriers and onset potential than those encountered for Pt‒C and Pt‒Ru.

Methanol Dehydrogenation to Methyl Formate Catalyzed by Cu/SiO2 Catalysts: Impact of Precipitation Procedure and Calcination Temperature

Methanol Dehydrogenation to Methyl Formate Catalyzed by Cu/SiO2 Catalysts: Impact of Precipitation Procedure and Calcination Temperature

Highly active methanol oxidation electrocatalyst based on 2D NiO porous nanosheets:a combined computational and experimental study

Two-dimensional (2D) nanostructures are attractive candidates for electrocatalytic applications owing to their excellent mechanical flexibility and large exposed surfaces. In this work, we present ultra-thin 2D NiO porous nanosheets prepared by a simple, economical and green experimental method (hydrothermal, freeze-drying, and sintering) as efficient electrocatalysts for direct methanol fuel cell (DMFC) application. Benefiting from the ultra-thin 2D framework and porous nanostructure, the 550-NiO catalyst (annealed at 550 °C) exhibit higher current density (12.54mA cm−2) and faster charge transfer in the catalytic process, due to its abundant solid state redox couples (Ni2+/Ni3+= 0.991), suitable oxygen defects and surface coverage of redox species (2.90 × 10−7mol cm−2). First-principles density functional theory calculations were employed to provide mechanistic insights into the methanol oxidation reaction over the NiO catalyst via methanol dehydrogenation to CO involving O–H and C–H bond scissions, and subsequently, CHO oxidation with OH. The most plausible reaction pathway of methanol oxidation on NiO (100) is predicted to be CH3OH → CH3O → CH2O → CHO → CHOOH → COOH → CO2. The reported facile, simple, low-cost and method provides an avenue for the rational design and synthesis of 2D NiO porous nanostructured electrode materials for DMFC and beyond.

Feature of catalysis on bimetallic alloys Zr with V, Mo, and Fe in the reaction of methanol oxidation

Catalytic behaviors of bimetallic catalysts-alloys of zirconium with vanadium, molybdenum, and iron was investigated in the oxidative dehydrogenation of methanol. The conditions for the formation of the catalyst’s active surface were revealed. The conversion of methanol into formaldehyde, dimethyl ether, and dimethoxymethane on bimetallic catalysts was studied. The characterization of catalysts was performed by XRD, XPS, and SEM. It was shown that the activity of samples increases after О2 + Н2 treatment and was associated with segregation of the active components of alloys (V, Mo) on the surface of catalysts and realization of their optimal oxidation state under catalysis conditions.

Active sites and effects of co-adsorbed H2O on isolated methanol dehydrogenation over Pt/γ-Al2O3

Dehydrogenation is the first reaction of the aqueous phase reforming (APR) mechanism of polyols, and its rate is likely affected by the environment at the active site. This study focuses on reactions of methanol on benchmark Pt/γ-Al2O3 catalysts probed by infrared spectroscopy under high vacuum. CO in linear and bridging coordination are the dominant surface species on metal sites. Pt particle sizes and reaction temperatures are varied to identify the kinetically preferred active site for methanol dehydrogenation as either lowly coordinated (edges, corners, interface) or highly coordinated (terraces) metal atoms. Interpretation of temperature-dependent IR spectra up to 450 °C show that larger Pt particles produce more CO at lower temperatures from complete methanol dehydrogenation. Similarly, time-resolved isothermal experiments at 150 °C showed equilibrium conversion occurred much faster on larger Pt particles than smaller ones. Features of evolving ν(C≡O) bands (shape, vibrational frequencies, integrals) suggest that, even on small Pt particles, CO first forms on the scarcely available terraces, or possibly in the form of islands. We have thus experimentally identified highly coordinated Pt metal as the more active site in overall methanol dehydrogenation. The electronic and chemical effects of co-adsorbed water and hydrogen on dehydrogenation activity and the CO spectra are discussed. The co-adsorption of water, an abundant APR component needed for the water-gas shift reaction, does not appear to affect methanol dehydrogenation on large Pt particles but hinders the reaction on small Pt particles as evident by limited growth in the respective ν(C≡O) bands.

A mechanistic periodic DFT study of CH, CO, and OH dissociations in methanol: M-doped carbon nanotubes (M=Pt, B, Al, N, P) versus Pt(100), Pt(110) and Pt(111) surfaces

• CO, CH, and OH dissociations in methanol are studied by using Pt(100), Pt(110), Pt(111), and doped CNT. • Dissociations are studied from both thermodynamics and kinetics points of view. • Theory shows that proposed SACs have less barrier energy for C−O dissociation compared to pure Pt surfaces. Periodic density functional theory is used to study adsorption and first step dissociation of methanol on M-doped carbon nanotubes (M = B, Al, Pt, N, and P) as a single atom catalyst (SAC). Data are compared with the adsorption and dissociation of methanol on Pt(100), Pt(110), and Pt(111). Only the first step of methanol dehydrogenation is investigated by considering three models of dissociations containing CH 3 + OH, CH 3 O + H, and CH 2 OH + H. The second model of dissociation is endothermic on all facets of Pt catalyst, but exothermic on B-, Al-, and Pt-doped carbon nanotube. The model of dissociation of CH 2 OH + H is more thermodynamically favorable on Pt(100), Pt(111), and Pt-doped carbon nanotube comparing to two other models. The most exothermic reaction belongs to the CH 3 + OH model on Al-doped carbon nanotube with -1.00 eV energy. Transition state calculations show that the barrier energy of C‒O dissociation on Al-doped carbon nanotube is 1.55 eV which is less than the barrier energies of C‒O dissociation on Pt(100), Pt(110), and Pt(111) which are 2.29, 2.45, and 1.96 eV. This shows that Al-doped carbon nanotube is a good candidate for alkylation catalyst. On the other hand B-doped carbon nanotube is a good non-metal catalyst for hydrogen production through O‒H dissociation.

Insights into the Mechanism of Methanol Steam Reforming Tandem Reaction over CeO2 Supported Single-Site Catalysts.

We demonstrated how the special synergy between a noble metal single site and neighboring oxygen vacancies provides an "ensemble reaction pool" for high hydrogen generation efficiency and carbon dioxide (CO2) selectivity of a tandem reaction: methanol steam reforming. Specifically, the hydrogen generation rate over single site Ru1/CeO2 catalyst is up to 9360 mol H2 per mol Ru per hour (579 mLH2gRu-1s-1) with 99.5% CO2 selectivity. Reaction mechanism study showed that the integration of metal single site and O vacancies facilitated the tandem reaction, which consisted of methanol dehydrogenation, water dissociation, and the subsequent water gas shift (WGS) reaction. In addition, the strength of CO adsorption and the reaction activation energy difference between methanol dehydrogenation and WGS reaction play an important role in determining the activity and CO2 selectivity. Our study paves the way for the further rational design of single site catalysts at the atomic scale. Furthermore, the development of such highly efficient and selective hydrogen evolution systems promises to deliver highly desirable economic and ecological benefits.

Grafting of Alkali Metals on Fumed Silica for the Catalytic Dehydrogenation of Methanol to Formaldehyde

AbstractWater free, non‐oxidative catalytic dehydrogenation of methanol to formaldehyde is an important process for the formation of anhydrous, molecular formaldehyde (FA). Sodium or sodium‐containing salts were shown to catalyze the reaction, but their reaction mechanism remains unclear. In this work, we thus investigated the performance of a series of catalysts prepared by grafting of alkali metals on amorphous silica for methanol catalytic dehydrogenation. The resulting catalysts displayed an increased activity for the catalytic dehydrogenation of methanol. Variation of the electron density of the supported alkali metal cations severely affected the FA selectivity, which followed the trend: Li>Na>K>Rb>Cs. A large gap in selectivity towards FA between ions with a high (i. e., Li, Na) and low charge density (i. e., K, Rb, Cs) was observed. Also, increased metal loading adversely affected FA selectivity and resulted in a larger production of carbon monoxide. Sodium grafted on silica yielded the best combination of moderate conversion and high selectivity.

The catalytic activity of PtnCum (n= 1-3, m= 0-2) clusters for methanol dehydrogenation to CO.

A large number of experiments show that PtCu catalyst has a good catalytic effect on methanol decomposition. Therefore, density functional theory (DFT) was used to further study the dehydrogenation of methanol catalyzed by PtnCum (n= 1-3, m= 0-2). The energy diagrams of O-adsorption path and H-adsorption path were drawn. By calculation, the Pt is the active site of the whole reaction process, and the barrier energy of the rate-determining step is 11.09kcalmol-1 by Pt2Cu, which is lower than that of Pt3 and PtCu2. However, the complete dehydrogenation product of methanol, CO, is easier to dissociate from PtCu2 clusters than from Pt3 and Pt2Cu clusters. Therefore, Cu doping can improve the catalytic activity and anti-CO toxicity of Pt to a certain extent.

Photocatalytic Production of Methyl Formate by Methanol Self-Coupling: From Oxidative Dehydrogenation to Direct Dehydrogenation

Photocatalytic production of methyl formate (MF) by methanol direct dehydrogenation under an inert Ar atmosphere with Pd/TiO2 as photocatalyst was realized in the present work. For comparison, experiments of the oxidative dehydrogenation under a CO2 atmosphere were also conducted. The production rates of H2 in the gaseous product and MF in the liquid-phase product under different atmospheres were compared. Intermediates involved in the dehydrogenation processes were characterized by in situ DRIFTS analysis; on the basis of the results, a new mechanism of MF generation from methanol dehydrogenation was proposed: methanol successively breaks the O–H bond and C–H bond to form adsorbed formaldehyde, which then reacts with undissociated methanol to form MF rather than dimerize with another formaldehyde. In addition, it was evidenced that during the dehydrogenation in CO2, the intermediate formate derived from the reduction of CO2 further reacts with methanol to increase the production rate of MF.

Partial oxidation of methanol to formaldehyde in an annular reactor

A structured reactor with annular configuration was applied for studying methanol oxidation to formaldehyde over silver. By eliminating gas phase reactions, high formaldehyde selectivity (93–97%) was obtained at low methanol and oxygen conversion under practically isothermal reaction conditions. CH2O and CO2 were the only carbon containing products, and both may be claimed as primary products along with H2. It also proves that CO is formed by homogenous decomposition of CH2O and should not be considered a main precursor to CO2, as assumed in several reaction mechanisms. The analysis of H2/CO2 ratio as a function of temperature provides an estimate of contributions from dehydrogenation and partial oxidation of methanol, and clearly suggests presence of a dehydrogenation pathway to CH2O. Extracting kinetic parameters is challenging due to a correlation between activity, oxygen dissolution, and silver restructuring and morphology and its dependence on temperature. Nevertheless, the data indicate 1st order with respect to oxygen. Conditioning by reaction at high temperature followed by a temperature ramp was performed to minimize the impact of a gradually changing Ag catalyst. The resulting Arrhenius analysis implies two distinct regions of activity. The apparent activation energy was estimated to 41 kJ/mol for the high temperature region, a value close to the activation energy for oxygen diffusion in silver at high temperature. The investigation demonstrates benefits of using an annular reactor configuration in bridging lab scale investigations with industrial conditions. Collecting reaction data at low oxygen conversion is enabled, which has not been achievable in conventional lab scale reactors this far.

Cobalt(II)porphyrin-Mediated Selective Synthesis of 1,5-Diketones via an Interrupted-Borrowing Hydrogen Strategy Using Methanol as a C1 Source.

A novel cobalt(II)porphyrin-mediated acceptorless dehydrogenation of methanol is reported for the first time. This methodology has been applied for the coupling of a variety of ketones with methanol to produce 1,5-diketones along with H2 and H2O as the environment friendly byproducts. This paradigm was also demonstrated for a one-pot synthesis of substituted pyridines using a sequential addition protocol where the 1,5-diketones were generated in situ. From many experiments including those involving deuterium labeling, it is proposed that protonated cobalt(II)porphyrin methoxide complex acts as an intermediate to generate formaldehyde along with a metal hydride.

Cu Nanocluster-Loaded TiO2 Nanosheets for Highly Efficient Generation of CO-Free Hydrogen by Selective Photocatalytic Dehydrogenation of Methanol to Formaldehyde.

Safe storage and transportation of H2 is a fundamental requirement for its wide applications in the future. Controllable release of high-purity H2 from a stable storage medium such as CH3OH before use offers an efficient way of achieving this purpose. In our case, Cu nanoclusters uniformly dispersed onto (001) surfaces of TiO2 nanosheets (TiO2/Cu) are selectively prepared by thermal treatment of HKUST-1 loaded TiO2 nanosheets. One of the TiO2/Cu composites, TiO2/Cu_50, exhibits remarkably high activity toward the selective dehydrogenation of CH3OH to HCHO with a H2 evolution rate of 17.8 mmol h-1 per gram of catalyst within a 16-h photocatalytic reaction (quantum efficiency at 365 nm: 16.4%). Theoretical calculations reveal that interactions of Cu nanoclusters with TiO2 could affect their electronic structures, leading to higher adsorption energy of CH3OH at Ti sites and a lower barrier for the dehydrogenation of CH3OH by the synergistic effect of Cu nanoclusters and TiO2, and lower Gibbs free energy for desorption HCHO and H2 as well.

Analysis of integrated system for ammonia synthesis and methyl formate production in the thermally coupled reactor

In this study, the simultaneous production of ammonia and methyl formate (MF) in a thermally coupled reactor has been investigated. Since the ammonia synthesis reaction is associated with heat release, and the production of MF is an endothermic reaction, the ammonia production reaction supplies the heat required for MF's reaction in the proposed reactor. To justify the suggested model's accuracy, the results are verified with the same condition's experimental data. This reactor's benefits include the elimination of ammonia synthesis inter-stage coolers, and reduced energy consumption. Also, exchanged heat causes significant improvements in both equilibrium reactions and enhanced process performance. On the other hand, by the novel configuration reactor, the methanol dehydrogenation reaction's hydrogen supplied about 21.57% of the required hydrogen in ammonia production feed. Eventually, the effect of input parameters on reactor performance investigates by using the sensitivity analysis and optimization process. It also found that about 34.66% of required hydrogen in ammonia synthesis feeds by methanol dehydrogenation reaction in optimum conditions supplied.

Highly active CuZn/SBA-15 catalyst for methanol dehydrogenation to methyl formate: Influence of ZnO promoter

• The catalytic performance of x CuZn/SBA-15 was dramatically superior to Cu/SBA-15. • The activity of x CuZn/SBA-15 in methanol dehydrogenation to MF was affected by ZnO amount. • The appropriate ZnO amount improved Cu dispersion and Cu 0 /(Cu 0 +Cu + ) ratio. • 10CuZn/SBA-15 exhibited most excellent activity along with favorable stability. Stable and efficient Cu/SBA-15 and x CuZn/SBA-15 ( x = 5, 10 and 15) in methanol dehydrogenation to methyl formate (MF) are prepared through a double-solvent impregnation (DI) method. Among all catalysts, 10CuZn/SBA-15 shows the highest catalytic performance with selectivity to MF about 88.1 % and methanol conversion of 31.1 %, which is attributed to the well-dispersed Cu particles and high ratio of Cu°/(Cu° + Cu + ). The proper amount of ZnO could improve dispersion of Cu because of its geometrical spacer, inhibiting growth of Cu particle, and the best dispersion is achieved in 10CuZn/SBA-15. Furthermore, the Cu°/(Cu° + Cu + ) ratio is greatly promoted with the assistance of ZnO, attributed to Cu-ZnO interaction, which reaches maxima of 53.3 % at a Cu/Zn mole ratio of 10. Specially, the optimized catalyst shows evident suitability at high temperature for methanol dehydrogenation reactions along with high level of conversion and selectivity for 100 h. Overall, our findings reveal that modification by the appropriate amount of ZnO in Cu-based catalyst has a positive impact on obtaining MF for the methanol dehydrogenation.

Dependence on Size of Supported Rh Nanoclusters in the Dehydrogenation of Methanol-d4 Obstructed by CO.

The size effect on the activity of a catalyst has been a focal issue since ideal catalysts were pursued, whereas that on the degradation of a catalyst, by reaction intermediates such as CO, is little discussed. We demonstrate that the dehydrogenation of methanol-d4 on supported Rh nanoclusters precovered with CO (Rh-CO clusters) was obstructed, indicated by a decreased production of CO and D2; the obstructive effect exhibits a remarkable dependence on the cluster size, with a minimum at a cluster diameter near 1.4 nm. The decreased production arose from a decreased reaction probability controlled by the increased activation energy for each dehydrogenation step (including formation of methoxy-d3), adsorption energies of CO, and repulsion from the CO array on the Rh-CO surface. The effects of these factors in deactivating the clusters varied separately with the cluster size. Consequently, the size effect on the CO poisoning should be taken into account in engineering the cluster size to optimize the catalytic performance.

Kinetic Evaluation of Deactivation Pathways in Methanol-to-Hydrocarbon Catalysis on HZSM-5 with Formaldehyde, Olefinic, Dieneic, and Aromatic Co-Feeds

Formaldehyde (HCHO), formed in situ by transfer dehydrogenation of methanol in methanol-to-hydrocarbon (MTH) conversion, reacts with other organic species including olefins, dienes, and aromatics t...

Unraveling the structure-activity relationships of Cu/H-BEA bifunctional catalyst for selective synthesis of dimethoxymethane by non-oxidative dehydrogenation of methanol

Oxymethylene ethers (OMEs) are synthetic fuels with excellent ability in reducing soot formation and good compatibility for diesel engines. Among OMEs, dimethoxymethane (DMM) is the simplest compound and its conventional production relies on an oxidative route leading to low H2 efficiency. Hence, recently, our group presented a H2 efficient gas-phase DMM synthesis route via nonoxidative dehydrogenation of methanol over Cu/Hβ. Herein, the role of Cu and Hβ are investigated by preparing Cu/Hβ catalysts with tailored properties. Highest DMM selectivity (81.5 %) was obtained over 1% Cu/Hβ-DeAl8 (Si/Al: 520). Besides, both calcined (consisting of Cu+) and reduced (consisting of Cu0) 1% Cu/Hβ-DeAl8 catalysts were active for DMM formation. Initial DMM selectivity reached 49 and 41 % for the calcined and in situ reduced catalysts, respectively, increasing to 75 % (calcined) and 81.5 % (reduced) after 1500 min TOS. The increased DMM selectivity relates to evolution of Cu species and changes with the amount of Lewis acidic sites.

Selective catalytic reduction of NOx in marine engine exhaust gas over supported transition metal oxide catalysts

The selective catalytic reduction (SCR) of nitrogen oxides (NOx) in the presence of methanol (methanol-SCR) was investigated over commercial oxide (γ-Al2O3 and TiO2) supported transition-metal oxide catalysts in lab scale. Of all the prepared catalysts, CuO/γ-Al2O3 catalyst exhibited the highest reduction efficiency in the methanol-SCR process. The practical test results in a marine engine further showed that the 2 wt% CuO/γ-Al2O3 catalyst can remove 93.9% of NOx without catalyst deactivation in several hours. Evidenced by relevant characterization results, the fast-redox properties of copper and rich acidic sites of γ-Al2O3 support were responsible for the excellent catalytic activity of the CuO/γ-Al2O3 catalyst. Revealed by In-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), formate-like species derived from methanol dehydrogenation act as the reaction intermediates for NOx reduction. Moreover, this work provides a novel process to reduce NOx and make use of adverse hydrocarbons in the flue gas simultaneously, opening a new research direction in NOx reduction technologies.