Ethanol Dehydrogenation Reaction Research Articles

Green hydrogen and acetaldehyde production via photo-induced thermal dehydrogenation of bioethanol over a highly dispersed CuS/ TiO2 catalyst

The emergence of global warming issues has triggered the interest in producing carbon-neutral energy sources and fossil-based chemicals from affordable and renewable feedstocks (e.g., bio-ethanol). Herein, the synthesis of highly dispersed CuS/TiO2 photothermal catalysts is reported for simultaneously converting ethanol into hydrogen and acetaldehyde under simulated sunlight. The catalyst achieved a hydrogen evolution rate of 51.61 mmol g−1 h−1 and an acetaldehyde production rate of 48.63 mmol g−1 h−1, with a maximal acetaldehyde selectivity of 97% among carbon-containing products. Compared to pristine TiO2, the introduction of plasmonic CuS largely extended the light adsorption range and enhanced the photothermal performance, whilst the formation of heterojunction structure improved the charge transfer and separation efficiency. The density functional theory calculation results demonstrate that CuS/TiO2 composite interfaces could significantly lower the activation energy of ethanol dehydrogenation reaction and improve hydrogen evolution reaction ability. This study provides deep insight into understanding and optimizing hot carrier dynamics in photothermal catalytic systems.

Single-Atom Alloy Formation via Reaction-Driven Catalyst Restructuring.

We demonstrate that single-atom alloy catalysts can be made by exposing physical mixtures of monometallic supported Cu and Pd catalysts to vinyl acetate (VA) synthesis reaction conditions. This reaction induces the formation of mobile clusters of metal diacetate species that drive extensive metal nanoparticle restructuring, leading to atomic dispersion of the precious metal, smaller nanoparticle sizes than the parent catalysts, and high activity and selectivity for both VA synthesis and ethanol dehydrogenation reactions. This approach is scalable and appears to be generalizable to other alloy catalysts.

Computational insights into the zeolite-supported gold nanocluster-catalyzed ethanol dehydrogenation to acetaldehyde.

Zeolite-supported gold nanoclusters play increasingly important roles in heterogeneous catalysis and exhibit unique catalytic properties for ethanol dehydrogenation to acetaldehyde. Nevertheless, the reaction mechanism and potential roles of the zeolite-encapsulated gold nanoclusters during the catalytic process remain unclear. Herein, computational studies were carried out to gain mechanistic insights into ethanol dehydrogenation to acetaldehyde under both aerobic and anaerobic conditions catalyzed by a silicalite-1 zeolite-encapsulated Au3 cluster cation (Au3+-S1). The presence of O2 can significantly promote the ethanol dehydrogenation catalyzed by Au3+-S1. A feasible mechanistic pathway could be initiated via the O2 induced H-atom transfer (HAT) step from the hydrogen of the hydroxyl group to afford ethoxy and OOH radical species. Subsequently, the OOH induced second HAT from α-C-H of the ethoxy intermediate could follow to afford the acetaldehyde product. Moreover, the possible confinement and stabilization effect of the zeolite channels on the ethanol dehydrogenation reaction was discussed.

Promoted hydrogen and acetaldehyde production from alcohol dehydrogenation enabled by electrochemical hydrogen pumps

The dehydrogenation reaction of bioderived ethanol is of particular interest for the synthesis of fuels and value-added chemicals. However, this reaction historically suffered from high energy consumption (>260 °C or >0.8 V) and low efficiency. Herein, the efficient conversion of alcohol to hydrogen and aldehyde is achieved by integrating the thermal dehydrogenation reaction with electrochemical hydrogen transfer at low temperature (120 °C) and low voltage (0.06 V), utilizing a bifunctional catalyst (Ru/C) with both thermal-catalytic and electrocatalytic activities. Specifically, the coupled electrochemical hydrogen separation procedure can serve as electrochemical hydrogen pumps, which effectively promote the equilibrium of ethanol dehydrogenation toward hydrogen and acetaldehyde production and simultaneously purifies hydrogen at the cathode. By utilizing this strategy, we achieved boosted hydrogen and acetaldehyde yields of 1,020 mmol g-1 h-1 and 1,185 mmol g-1 h-1, respectively, which are threefold higher than the exclusive ethanol thermal dehydrogenation. This work opens up a prospective route for the high-efficiency production of hydrogen and acetaldehyde via coupled thermal-electrocatalysis.

Investigation on deactivation of Cu-Cr catalyst for direct ethanol dehydrogenation to ethyl acetate, acetaldehyde, and hydrogen

BackgroundThe utilization of bioethanol by converting it into additional high-value-added products including acetaldehyde, ethyl acetate, and hydrogen impresses as an appealing strategy at the present. The Cu-Cr catalysts improved product formation on ethanol dehydrogenation. This research was to assess the stability of the reaction and the deactivation of the catalyst over protracted ethanol dehydrogenation. MethodsThe deactivation behaviors of 50 Cu-Cr catalyst on ethanol dehydrogenation reaction was investigated. The co-precipitation technique was used to synthesize the Cu-Cr catalyst, which was then reduced by a mixture of H2/N2 prior to the stability test in the ethanol dehydrogenation reaction. The fresh, reduced, and/or spent catalysts after being used in ethanol dehydrogenation were characterized using XRD, SEM-EDX, HR-TEM, H2-TPR, NH3-TPD, XPS, TGA, and TPO. Significant findingThe proportion of CuCr2O4, Cu+, and Cu0 active sites on the catalyst sample influenced catalytic activity. Based on the results, the activity was related to the oxidation state of copper-chromium in the Cu-Cr catalyst. Fascinatingly, the results of the ethanol dehydrogenation showed that the catalyst deactivation was caused by the change in the copper-chromium oxidation state via the hydrogen self-reduction process and the soft coke formation on active sites after prolonged ethanol dehydrogenation resulting in a decrease in catalytic activity.

Redispersion and Stabilization of Cu/MFI Catalysts by the Encapsulation Method for Ethanol Dehydrogenation

Encapsulation of metal particles with ordered porous zeolite is a promising method to stabilize nanoparticles. In this work, Cu/MFI catalysts prepared by the impregnation method were encapsulated with MFI to yield (Cu/MFI)@MFI catalysts for ethanol dehydrogenation. The encapsulation process not only anchored Cu particles into MFI but also redispersed Cu with decreased particle sizes and newly formed Cu+ species. During the ethanol dehydrogenation reaction, the Cu+ and Cu0 species confined in (Cu/MFI)@MFI catalysts demonstrated synergistic effects and afforded 95.7% acetaldehyde selectivity, 97.2% ethanol conversion at 523 K, and a weight hourly space velocity (WHSV) of 0.53 h–1 in the 200 h time on stream over the optimized (Cu/MFI)@MFI 100% catalyst, which is significantly better than the counterpart of the Cu/MFI catalyst.

Production of hydrogen from gas-phase ethanol dehydrogenation over iron-grafted mesoporous Pt/TiO2 photocatalysts

We report the photocatalytic activity of iron-grafted mesoporous Pt/TiO2 catalysts, combining the properties of heterojunction photocatalysts with mesoporosity, for the gas-phase production of hydrogen from water-ethanol mixtures. GC–MS analysis reveals a preferential ethanol dehydrogenation reaction pathway, resulting in the formation of acetaldehyde with high selectivity versus carbon dioxide, for all of the catalysts investigated. Multi-technique characterization reveals that, in all the iron-grafted samples, Fe is located predominantly on the surfaces of the catalysts as Fe2O3 rather than doping the anatase structure, while the mesoporosity of the starting TiO2 is preserved. Among the different materials, the activity for photocatalytic ethanol dehydrogenation is optimum in the catalyst with the lowest iron content. According to XPS and time-resolved fluorescence measurements, this can be accounted for by higher Fe surface dispersion and consequent efficient formation of a surface heterojunction between Fe2O3 and TiO2 that favours charge separation.

Tracing the reactivity of single atom alloys for ethanol dehydrogenation using ab initio simulations

A full DFT parameterized MKM is used to accurately predict the reactivity trend for ethanol dehydrogenation reaction on SAAs.

Copper-based catalysts for ethanol dehydrogenation and dehydrogenative coupling into hydrogen, acetaldehyde and ethyl acetate

Hydrogen is clean energy for the future and bio-hydrogen can be produced from bio-ethanol by dehydrogenation, and subsequent dehydrogenative coupling reactions. Two main products, acetaldehyde, and ethyl acetate, along with hydrogen are important industrial products from ethanol. In this work, we focus on the progress on the development of Cu-based catalysts for ethanol dehydrogenation and dehydrogenative coupling reactions The review discusses the effect of Cu charge, Cu particle size and dispersion, support, promoters and reaction conditions. This work found that the rate of ethanol consumption is different from the absolute ethanol conversion. Cu loading and Cu dispersion have a strong impact on the catalytic activity and the proper value are 10% and 20–60% for Cu loading and dispersion, respectively. The selectivity to acetaldehyde and ethyl acetate can be tailored by particle size, Cu oxidation, acidity/basicity of catalyst as well as contact time. This review will provide a full picture of the development of Cu-based catalysts for ethanol dehydration and has a significant impact on the field.

Insights into the Preparation of Copper Catalysts Supported on Layered Double Hydroxide Derived Mixed Oxides for Ethanol Dehydrogenation.

Acetaldehyde is an important chemical commodity and a building block for producing several other high-value products in the chemical industry. This has motivated the search for suitable, efficient, stable, and selective catalysts, as well as renewable raw materials such as ethanol. In this work, supported copper catalysts were prepared from CuZnAl layered double hydroxides (LDHs) with different copper contents (5, 10, and 20 wt %) for application in the ethanol dehydrogenation reaction (EDR). The samples were thoroughly characterized by a series of techniques, which allowed for analysis of all of the copper and zinc species involved in the different catalyst preparation steps and during the EDR. The results obtained by in situ quick extended X-ray absorption fine structure (EXAFS) measurements, combined with multivariate data analysis, showed that the copper content in the pristine LDH influenced the phase composition of the mixed oxide support, which consequently affected the dispersion of copper nanoparticles. The higher the copper content, the higher are the ZnAl2O4 and zinc tetrahedral prenuclei (TPN) contents, to the detriment of the ZnO content. All the samples showed high selectivity (>97%) and stability in the catalytic reactions at 300 and 350 °C, with no observed deactivation during 6 h on-stream. Although the samples with lower copper content presented higher copper dispersion and reactivity, the sample containing 20 wt % of copper outperformed the others, with greater conversion and higher activity toward acetaldehyde.

Effect of Adding Transition Metals to Copper on the Dehydrogenation Reaction of Ethanol

The present work aims to investigate the effect adding Ag, Co, Ni, Cd and Pt to copper on ethanol dehydrogenation. The catalysts synthesized by deposition–precipitation method were characterized using various physicochemical methods such as N2 adsorption–desorption, TPR, SEM–EDX, XRD, XPS and TGA–DSC-MS. Catalytic evaluation results revealed that the predominant product of the reaction was acetaldehyde. Monometallic copper or mixed with Cd, Ag or Co show good catalytic performances. Adding nickel to copper improves the process conversion but reduces acetaldehyde selectivity, giving rise to methane in produced hydrogen. Pt-Cu/SiO2 catalyst guides the reaction towards diethyl ether. Time on stream tests performed during 12 h at 260 °C, showed that adding Cd to Cu enhances its stability by over 30% of conversion, this is explained by the reduction of copper crystallites sintering, which makes Cd-Cu/SiO2 a promising catalyst for the production of acetaldehyde by ethanol dehydrogenation.

PEM fuel cells fed by hydrogen from ethanol dehydrogenation reaction: Unveiling the poisoning mechanisms of the by-products

This work investigates the influence of hydrogen contaminated with the main by-products of the ethanol dehydrogenation reaction, i.e. ethyl acetate, acetaldehyde and unreacted ethanol, on the anode performance of a proton exchange membrane fuel cell employing different catalysts, aiming at understanding and minimizing the efficiency losses caused by these molecules. Pt-W/C and Pt-Sn/C catalysts were investigated, having Pt/C as reference, which were chosen due their ability to oxidize small organic molecules without breaking of CC bonds and without producing strong poisoning intermediates (i.e. less prone to have its active sites blocked by side reactions). Results evidence that anode catalysts that presents lower activity for small organic molecules oxidation and/or weaker reactant adsorption, which is the case of Pt-Sn/C, are best suited for PEMFC systems directly fed by hydrogen from ethanol dehydrogenation reaction. It is also found that crossover of the considered by-products from the anode towards the cathode also has a major impact on fuel cell efficiency losses.

Conversion of ethanol to 1,3–butadiene over Ag–ZrO2/SiO2 catalysts: The role of surface interfaces

Abstract A series of Ag–ZrO2/SiO2 catalysts with different metal–support interfaces were synthesized in an effort to elucidate the roles of specific interfaces in controlling the ethanol to 1,3–butadiene conversion and selectivity. According to the results of detailed characterizations (e.g. CO/pyridine–DRIFTS, XPS, TEM, NH3–TPD, and 1H MAS NMR), it was found that the Ag–O–Si interfaces significantly enhanced the dehydrogenation of ethanol while the presence of ZrO2 improved the interaction between Ag and ZrO2/SiO2, creating more Agδ+ active sites. The high dispersion of ZrO2 on SiO2 generated abundant Zr–O–Si interfaces with medium and weak Lewis acidity, promoting the condensation of acetaldehyde to crotonaldehyde. These Zr–O–Si interfaces in close interaction with Agδ+ species played a critical role in the enhanced H transfer during the MPV reduction of crotonaldehyde to crotyl alcohol. The synergies among the interfaces resulted in retarded ethanol dehydration reactivity, balanced ethanol dehydrogenation and condensation reactions, and a subsequent high 1,3–butadiene yield.

Concomitant Production of Hydrogen, Sodium Acetate, and Polymerized Species from Non-Catalytic Ethanol Dehydrogenation

A detailed study of the production of hydrogen and high added-value liquid products from the ethanol dehydrogenation reaction in the presence of sodium hydroxide (10% m m-1) was undertaken. Experiments were carried out in a batch reactor under different reaction conditions (temperature of 240 oC and autogenous pressure between 45 and 72 bar), with analysis of the products obtained in the gas, liquid and solid fractions. The results showed that hydrogen was the major product formed in the gaseous fraction (maximum of 86.9%), while sodium acetate was the product in the solid fraction. Studies of the reaction mechanisms confirmed formation of the products identified in the gaseous and solid fractions. Mass spectrometry analyses of the liquid fractions revealed the presence of a series of compounds with molecular masses considerably higher than that of ethanol, which could be explained by the favoring of anionic polymerization reactions, under the experimental conditions employed.

Comparative study of Cu, Ag and Ag-Cu catalysts over graphite in the ethanol dehydrogenation reaction: Catalytic activity, deactivation and regeneration

The physicochemical and catalytic properties of bimetallic AgCu catalysts and their monometallic counterparts supported on a high surface area graphite have been comparatively evaluated in the ethanol dehydrogenation reaction, performed in a continuous-flow reactor. While Cu was incorporated by the incipient wetness impregnation technique, for Ag catalysts two synthesis procedures were explored: incipient wetness impregnation and adsorption of Tollens’ reagent. The catalysts prepared by wetness impregnation exhibited higher metal dispersion, being improved for the bimetallic catalysts in comparison with the monometallic counterparts. The results obtained in the catalytic tests revealed that Cu catalysts is nearly two orders of magnitude more active than Ag catalyst in the dehydrogenation reaction of ethanol on either a turnover frequency or a weight basis, but at the same time both catalysts were 100% selective to acetaldehyde. Whereas selectivity was not affected by the bimetallic composition, there was a substantial decrease in the reaction rate among the bimetallic catalysts as the Cu/Ag ratio diminished, due to blockage of copper surface active sites by silver. Both silver and copper, and the bimetallic catalysts, suffered from deactivation at 523 K, caused by blocking of active sites by adsorbed hydrocarbons on the catalyst surface (fouling). Carbonaceous deposits were removed through a thermal treatment under H2 flow, which allowed the total recovery of the initial catalytic activity.

Electrochemical promotion for hydrogen production via ethanol steam reforming reaction

In this work we have investigated for the first time the electrochemical activation of a catalyst for the ethanol reforming reaction. For that purpose, a Pt-KβAl2O3 electrochemical catalyst has been prepared, characterized and tested under ethanol reforming reaction conditions. The electrochemically supply of potassium ions under negative polarization step, strongly increased the hydrogen production rates leading to a reversible and controllable promotional effect. It has been attributed to the enhancement of the kinetic of ethanol dehydrogenation reaction, due to the strengthening of the chemisorptive bond of intermediate ethoxy molecules. It will increase the stability of this intermediate, thus favoring its formation, which initiates the ethanol reforming process. However, a large amount of carbonaceous species were formed on the catalyst surface during the negative polarization step that causes a continuous decrease in the catalytic activity under long polarization times. Under these conditions, the application of a catalyst potential of 2 V leads to a complete removal of the previous deposited carbonaceous molecules which allows further electrochemical activation steps. The obtained catalytic results have been supported by in-situ temperature programmed oxidation analysis and ex-situ Raman spectroscopy and Scanning Electron Microscopy. These techniques, in conjunction with the obtained catalytic results, have demonstrated the interest of the EPOC phenomenon for in-situ tuning the adsorption of reactants molecules on catalyst surface and its application in the hydrogen production technology, improving catalyst conversion and selectivity.

Copper‐Basic Sites Synergic Effect on the Ethanol Dehydrogenation and Condensation Reactions

AbstractBioethanol upgrading through condensation is of key interest in the development of sustainable processes, shifting from fossil to renewable carbon. Here, a new strategy is proposed, which combines in one catalyst an appropriate distribution of acid/basic sites of a mixed oxide with the presence of an active dehydrogenation phase (Cu nanoparticles). Experiments, performed in a fixed bed reactor, reveal a very positive effect of Cu in the performance of Mg−Al catalyst, with 1‐butanol productivity 12 times higher at 523 K under inert conditions. The improvement is even more notable in presence of H2, almost 30 times higher, under same conditions. The presence of Cu on the surface increases the formation of acetaldehyde, limiting the extent of dehydration side‐reactions. In addition, hydrogen enhances the C4 hydrogenation, preventing oligomerizations and inhibiting decarbonylation steps that are directly related to the catalytic deactivation by poisoning.

Effect of the SiO2 support on the catalytic performance of Ag/ZrO2/SiO2 catalysts for the single-bed production of butadiene from ethanol

A ternary Ag/ZrO2/SiO2 catalyst system was studied for single-step conversion of ethanol to butadiene by varying the catalyst composition (Ag, Ir, or Pt metal component, Ag/ZrO2 loading, and choice of SiO2 support) and operating conditions (space velocity and feed gas composition). Exceptional catalytic performance was achieved over a 1%Ag/4%ZrO2/SiO2-SBA-16 catalyst leading to 99% conversion and 71% butadiene selectivity while operating under mild conditions (325 °C, 1 atm, and 0.23 h−1). Several classes of silica—silica gels, fumed silicas, mesoporous silicas)—were evaluated as catalyst supports, and SBA-16 was found to be the most promising choice. The SiO2 support was found to significantly influence both conversion and selectivity. A higher SiO2 catalyst surface area facilitates increased Ag dispersion which leads to greater conversion due to the accelerated initial ethanol dehydrogenation reaction step. By independently varying Ag and ZrO2 loading, Ag was found to be the main component that affects ethanol conversion. ZrO2 loading and thus Lewis acid sites concentration was found to have little impact on the ethanol conversion. Butadiene selectivity depends on the concentration of Lewis acid site, which in turn differs depending on the choice of SiO2 support material. We observed a direct relationship between butadiene selectivity and concentration of Lewis acid sites. Butadiene selectivity decreases as the concentration of Lewis acid sites increases, which corresponds to an increase in ethanol dehydration to ethylene and diethyl ether. Additionally, adding H2 to the feed had little effect on conversion while improving catalytic stability; however, selectivity to butadiene decreased. Finally, catalyst regenerability was successfully demonstrated for several cycles.

NiCu single atom alloys catalyze the C[sbnd]H bond activation in the selective non- oxidative ethanol dehydrogenation reaction

NiCu single atom alloy (SAA) nanoparticles supported on silica are reported to catalyze the non-oxidative dehydrogenation of ethanol, selectively to acetaldehyde and hydrogen products by facilitating the CH bond cleavage. The activity and selectivity of the NiCu SAA catalysts were compared to monometallic copper and to PtCu and PdCu single atom alloys, in a flow reactor at moderate temperatures. In-situ DRIFTS showed that the silica support facilitates the OH bond cleavage of ethanol to form ethoxy intermediates over all the supported alloy catalysts. However, these remain unreactive up to 250 °C for the Cu/SiO2 monometallic nanoparticles, while in the NiCu SAA, acetaldehyde is formed at much lower temperatures, below 150 °C. In situ DRIFTS was also used to identify the CH activation step as the rate determining step of this reaction on all the copper catalysts we examined. The presence of atomically dispersed Ni in Cu significantly lowers the CH bond activation barrier, whereas Pt and Pd atoms were found less effective. This work provides direct evidence that the CH bond cleavage is the rate determining step in ethanol dehydrogenation over this type catalyst.

Dehydrogenation of ethanol over carbon-supported Cu–Co catalysts modified by catalytic chemical vapor deposition

A bimetallic copper–cobalt catalyst supported on activated carbon fibrous (ACF) material was prepared by the incipient wetness impregnation of the support with an aqueous solution of corresponding nitrates. Reference monometallic Cu/ACF and Co/ACF samples were synthesized analogously. In order to enhance the metal-support interaction and stabilize the dispersion of active components, the Cu–Co/ACF catalyst was subjected to catalytic chemical vapor deposition of ethylene at 600 °C with the formation of carbon nanofibers (CNF). As a result, the catalytic system consisting of Cu–Co particles anchored on carbon–carbon composite was obtained. All samples were characterized by a set of physicochemical methods. The catalytic performance of pristine and CNF-modified samples was studied in the ethanol dehydrogenation reaction. The activity of Cu–Co/CNF/ACF catalyst was shown to be two times higher compared with the unmodified bimetallic sample.