Activity For Water Gas Shift Reaction Research Articles

Controlling Mechanism of the Water–Gas Shift Reaction Activity Catalyzed by Au Single Atoms Supported on Multicomponent Oxides

Controlling Mechanism of the Water–Gas Shift Reaction Activity Catalyzed by Au Single Atoms Supported on Multicomponent Oxides

High-area alumina supported Cu-Ce atomic species for water-gas shift reaction.

Atomically dispersed cerium species, anchored to high-area alumina by unsaturated penta-coordinated aluminum, strongly interact with atomically dispersed Cu species to provide active centers for water-gas shift reaction (WGSR). The alumina-anchored Ce3+ species stabilize atomically dispersed Cu+ to form Cu+-Ce3+ active complexes and they work synergistically to enhance low-temperature WGSR activity. This work offers alternative approaches to developing low-cost catalysts for the WGSR process.

Migration and aggregation of Pt atoms on metal oxide-supported ceria nanodomes control reverse water gas shift reaction activity

Single-atom catalysts (SACs) are particularly sensitive to external conditions, complicating the identification of catalytically active species and active sites under in situ or operando conditions. We developed a methodology for tracing the structural evolution of SACs to nanoparticles, identifying the active species and their link to the catalytic activity for the reverse water gas shift (RWGS) reaction. The new method is illustrated by studying structure-activity relationships in two materials containing Pt SACs on ceria nanodomes, supported on either ceria or titania. These materials exhibited distinctly different activities for CO production. Multimodal operando characterization attributed the enhanced activity of the titania-supported catalysts at temperatures below 320 ˚C to the formation of unique Pt sites at the ceria-titania interface capable of forming Pt nanoparticles, the active species for the RWGS reaction. Migration of Pt nanoparticles to titania support was found to be responsible for the deactivation of titania-supported catalysts at elevated temperatures. Tracking the migration of Pt atoms provides a new opportunity to investigate the activation and deactivation of Pt SACs for the RWGS reaction.

Investigation of the promotion effect of metal oxides on the water-gas shift reaction activity over Pt-MOx/CeO2 catalysts for aqueous phase reforming

Aqueous phase reforming (APR) of methanol is a potential pathway for the effective hydrogen production under relatively mild conditions. The Pt/CeO2 and a series of Pt-MOx/CeO2 (M = Fe, Cr, Mg, Mn) catalysts were prepared by sequential impregnation method and their APR reaction performances were studied. The catalyst properties including valence state of the promoters, the amount of oxygen vacancies, the metal distributions, the adsorption properties of CO and the acidity/basicity of catalysts were characterized and analyzed by XPS, XRD, TEM, CO-TPD, NH3-TPD, CO2-TPD, etc. It was found that the addition of MOx weakened the Pt-CeO2 interaction and promoted the generation of Ptδ+ species with lower valence state, which contribute to the C–H bond cleavage and facilitate methanol conversion. The highest hydrogen production (164.78 mmol) and relatively low CO and CH4 selectivities were obtained over the Pt-MgO/CeO2, while the highest CH4 selectivity was obtained over the Pt-CrOx/CeO2 (2.21%). Over the Pt/CeO2 and Pt-MOx/CeO2 (M = Fe, Cr, Mg, Mn) catalysts, CO2/CH4 ratio correlated well with the catalyst basicity, indicating that the basicity promotes the dissociation adsorption of H2O as well as the water-gas shift (WGS) reaction activity and decreases the methanation activity.

NiCx/Ni-foam discovered as a promising high-temperature WGSR catalyst

Water gas shift reaction (WGSR) is urgently calling for an alternative to the Fe-Cr catalyst. Ni-based catalysts are taken into consideration but remain challenging because of their high methanation activity. Here we report a highly active and selective NiCx/Ni-foam catalyst with clearly detectable Ni3C phase, facilely obtainable by endogenous growth of NiC2O4 onto a Ni-foam and subsequent H2-reduction treatment. The preferred catalyst with high content of NiCx is capable of converting 63.6% or 94.3% CO at 350 °C or 400 °C with trace or < 0.8% CH4 formation for a feed gas with H2O/CO/Ar molar ratio of 4/1/9, and is stable for at least 110 h. It is experimentally and theoretically unveiled that the Ni3C facilitates the dissociative activation of H2O and favors CO to form carboxylate species (favorable for CO2 formation) rather than active Ni(CO)n intermediates for CH4 formation thereby enabling the catalyst with high WGSR activity and selectivity.

Coordination-number-determined activity of copper catalyst in water-gas shift reaction

The water–gas shift reaction (WGSR) is of great significance in industrial hydrogen production. In this paper, Cun/TiO2(n = 1,2,4,8) and Cu (111) crystal planes were studied to explore the effect of size effect on the activity of WGSR. Density functional theory (DFT) calculations showed that the adsorption energy of H2O molecule was significantly enhanced on the surface of Cu1 and Cu2 clusters compared with Cu4 and Cu8 clusters, while CO adsorption strength first increased and then decreased. Among many copper clusters of different sizes, the redox pathway cannot proceed due to the lack of active sites on Cu1 and Cu2 clusters. According to the analysis of the microkinetic model, the order of WGSR activity on the surface of copper clusters of different sizes is: Cu4 > Cu2 ≈ Cu8 > Cu1 > Cu (111). The active center structure of the copper cluster is composed of 3 copper atoms in which the Cu-Cu coordination number is ca. 2 ∼ 3, and the active center is partially oxidized copper. Essentially, the low-coordination copper atoms determined by the geometry structure promote the WGSR activity of the copper clusters. This work not only reveals the copper cluster size effect on WGSR, but also provides the guidance for the size design and control of other supported metal catalysts.

Nanotubular Pt-loaded TiO2 catalysts with vanadium-doping to enhance water–gas shift reaction activity

By utilizing shape control and metal-doping techniques, the dispersion of loaded metal and the H2O dissociation ability were significantly improved, resulting in a more sustainable and efficient hydrogen production via the water–gas shift reaction.

Effects of Sn Promoter on the Ordered Mesoporous Co3O4-Al2O3 Mixed Metal Oxide for Fischer–Tropsch Synthesis Reaction

The highly ordered mesoporous Co3O4-Al2O3 bimetal oxide, prepared by a nano-casting method, was modified with Sn promoter (denoted as Sn/m-CoAlOx) to enhance selectivity to liquid-hydrocarbons as well as to suppress CO2 formation formed by a water gas-shift (WGS) reaction activity during CO hydrogenation to hydrocarbons (Fischer–Tropsch Synthesis (FTS) reaction). Based on the surface properties of the Sn/m-CoAlOx in the range of 0.25–0.65 wt%Sn, the Sn promoter generally decreased CO conversion and increased C5+ selectivity through its non-selective blockages of the active metallic cobalt sites, which were responsible for more difficult reducibility of cobalt nanoparticles with an increase of Sn content as well. In addition to those contributions of Sn promoter, the decreased CO2 and CH4 selectivity was clearly observed on the optimal Sn(2)/m-CoAlOx with only small decrease of CO conversion with 79.1% from 81.5% for the reference m-CoAlOx. Those phenomena were mainly attributed to the suppressed WGS reaction activity as well as the decreased hydrogenation activity to form CH4 due to the suppressed H2 adsorption capacity on the less reduced surface Co sites on the Sn(2)/m-CoAlOx.

A systematic theoretical study the active sites of potassium promoter on the activity of water-gas shift reaction over Pt(1 1 1)

Alkali metals play an important role as promoters in heterogeneous catalytic reactions, but the systematic study of the nature (or active sites) of promoter is far away from enough. Thepossible active sites of potassium promoter such as metallic potassium (K), hydroxyl species stabilized potassium (KOH), and partially oxidized potassium (K2O) species on the Pt-catalyzed water–gas shift reaction (WGSR) wassystematically theoretical studied in this work. The calculation results indicated that the adsorption strength follows the trend K2O/Pt(111) > KOH/Pt(111) ≈ K/Pt(111) > Pt(111), and the K2O additive enhances the adsorption properties largest because of more K ions can be availed to bind with adsorbed species. On the other hand, the promotion effect for WGSR with the order: KOH/Pt(111〉 K2O/Pt(111) > K/Pt(111) ≈ Pt(111), and the KOH species displays the promising promotion effect due to the facile of O–H/C–H bond cleavage as well as the C-O bond formation. Interestingly, it was shown that the high promotion effect of KOH (or K2O) on WGSR is related to the strong activation properties of water dissociation assisted by the OH (or O) group involved in KOH (or K2O). It might be pointed out that the metallic K additive atoms almost have no promotion effect on the Pt-catalyzed WGSR owing to the more difficult in the formation of C-O bond formation compared to that of pure Pt(111), and the active site of potassium promoter is the KOH-like species. The promotion properties of potassium on the adsorption strength of oxygen-containing species such H2O could be ascribed to the strong short-ranged direct interaction between the K-species through space. Microkinetic modeling analysis indicated that the carboxyl mechanism is the dominant mechanism of the whole WGSR, followed by the redox mechanism and formate mechanism. It is desirable for that the present work may extend to the alkali promotion character on WGSR to other situation like metal oxide-supported metal clusters.

Heterostructured Ceria-Titania-Supported Platinum Catalysts for the Water Gas Shift Reaction.

The water gas shift (WGS) reaction is a key process in the industrial hydrogen production and the development and application of the proton exchange membrane fuel cell. Metal oxide-supported highly dispersed Pt has been proved as an efficient catalyst for the WGS reaction. In this work, a series of supported 0.5Pt/xCe-10Ti (x = 1, 3, or 5) catalysts with different Ce/Ti molar ratios were prepared by a simple deposition-precipitation method. Compared with single TiO2- or CeO2-supported Pt catalysts, it was found that the 0.5Pt/3Ce-10Ti catalyst showed an obvious advantage in activity for the WGS reaction. In this catalyst, dispersed CeO2 nanoparticles were supported on the TiO2 sheets, and Pt single atoms and nanoparticles were located on CeO2 and at the boundary of TiO2 and CeO2, respectively. It found that the reduction ability of the supported Pt catalyst was remarkably improved; meanwhile, the adsorption strength of CO on the surface of 0.5Pt/3Ce-10Ti was moderate. The heterostructured CeO2-TiO2 support gave an effective regulation on the Pt status and further influenced the CO adsorption ability, inducing excellent WGS reaction activity. This work provides a reference for the development and application of heterostructured materials in heterogeneous catalysis.

Water Gas Shift Reaction Activity on Fe (110): A DFT Study

Metal Fe is one of the phases existing on iron-based catalysts for a high-temperature water gas shift reaction (WGSR), but research on the activity of metal Fe in WGSR is almost not reported. In this work, the density functional theory (DFT) method was used to systematically study the reaction activity and mechanisms of WGSR on metal Fe (110), including the dissociation of H2O, the transformation of CO and the formation of H2, as well as the analysis of surface electronic properties. The results show that (1) the direct dissociation of H2O occurs easily on Fe (110) and the energy barrier is less than 0.9 eV; (2) the generation of CO2 is difficult and its energy barrier is above 1.8 eV; (3) H migrates easily on the Fe surface and the formation of H2 also occurs with an energy barrier of 1.47 eV. Combined with the results of Fe3O4, it can be concluded that the active phase should be Fe3O4 with O vacancy defects, and the iron-rich region plays an important role in promoting the formation of H2 in WGSR.

Improved Catalytic Activity of the High-Temperature Water Gas Shift Reaction on Metal-Exsolved La0.9Ni0.05Fe0.95O3 by Controlling Reduction Time

The catalyst exsolved from nickel-doped perovskite oxide, La0.9Ni0.05Fe0.95O3, has been proven to be effective for gas-phase reactions. To obtain the optimum amount of exsolved nanoparticles from the parent perovskite oxide, control of the reduction treatment condition is vital. Here, the effect of reduction time on the exsolved nanoparticle distribution, and thus the catalytic activity of the high-temperature water gas shift reaction (WGSR), was investigated. Upon conducting a wide range of characterizations, we assumed that the exsolution process might be a two-step process. Firstly, the surface oxygen is extracted. Secondly, due to the unstable perovskite structure, the Ni ions in the bulk La0.9Ni0.05Fe0.95O3 continuously diffuse toward the surface and, as the reduction progresses, more nuclei are generated to form a greater number of nanoparticles. This assumption is proven by the fact that, with an increase in the exsolution treatment time, the population of exsolution nanoparticles increases. Moreover, as the reduction time increases, the high-temperature WGSR activity also increases. The temperature-programmed measurements suggest that the exsolved nanoparticles are the active reaction sites. We believe that this study is helpful for understanding exsolution behavior during reduction treatment and, thus, developing a perovskite exsolution catalyst for the WGSR.

Design of Cobalt Fischer-Tropsch Catalysts for the Combined Production of Liquid Fuels and Olefin Chemicals from Hydrogen-Rich Syngas.

Adjusting hydrocarbon product distributions in the Fischer–Tropsch (FT) synthesis is of notable significance in the context of so-called X-to-liquids (XTL) technologies. While cobalt catalysts are selective to long-chain paraffin precursors for synthetic jet- and diesel-fuels, lighter (C10–) alkane condensates are less valuable for fuel production. Alternatively, iron carbide-based catalysts are suitable for the coproduction of paraffinic waxes alongside liquid (and gaseous) olefin chemicals; however, their activity for the water–gas-shift reaction (WGSR) is notoriously detrimental when hydrogen-rich syngas feeds, for example, derived from (unconventional) natural gas, are to be converted. Herein the roles of pore architecture and oxide promoters of Lewis basic character on CoRu/Al2O3 FT catalysts are systematically addressed, targeting the development of catalysts with unusually high selectivity to liquid olefins. Both alkali and lanthanide oxides lead to a decrease in turnover frequency. The latter, particularly PrOx, prove effective to boost the selectivity to liquid (C5–10) olefins without undesired WGSR activity. In situ CO-FTIR spectroscopy suggests a dual promotion via both electronic modification of surface Co sites and the inhibition of Lewis acidity on the support, which has direct implications for double-bond isomerization reactivity and thus the regioisomery of liquid olefin products. Density functional theory calculations ascribe oxide promotion to an enhanced competitive adsorption of molecular CO versus hydrogen and olefins on oxide-decorated cobalt surfaces, dampening (secondary) olefin hydrogenation, and suggest an exacerbated metal surface carbophilicity to underlie the undesired induction of WGSR activity by strongly electron-donating alkali oxide promoters. Enhanced pore molecular transport within a multimodal meso-macroporous architecture in combination with PrOx as promoter, at an optimal surface loading of 1 Prat nm–2, results in an unconventional product distribution, reconciling benefits intrinsic to Co- and Fe-based FT catalysts, respectively. A chain-growth probability of 0.75, and thus >70 C% selectivity to C5+ products, is achieved alongside lighter hydrocarbon (C5–10) condensates that are significantly enriched in added-value chemicals (67 C%), predominantly α-olefins but also linear alcohols, remarkably with essentially no CO2 side-production (<1%). Such unusual product distributions, integrating precursors for synthetic fuels and liquid platform chemicals, might be desired to diversify the scope and improve the economics of small-scale gas- and biomass-to-liquid processes.

Characteristics and performance of the Co–CeO2 catalyst as a function of the promoter (La, Pr, and Zr) used in high temperature water gas shift reaction

The catalysts used to facilitate the water gas shift reaction (WGSR) are generally harmful to the environment. Therefore, catalysts that have high activity and stability in WGSR and do not pollute the environment need to be fabricated. Herein, three promoters (La, Pr, and Zr) are added into Co–CeO2 (CoCe) catalyst to improve catalytic performance in a high temperature WGSR to produce high-purity hydrogen from waste-derived synthesis gas. Various techniques are employed to confirm the changes in the properties that affect the catalytic performance. The catalytic reaction is performed at a high gas hourly space velocity to screen the performance of the promoted CoCe catalysts. The CoCeZr catalyst shows the highest CO conversion (XCO = 88% at 450 °C) due to its high Co dispersion and oxygen vacancy resulting from the addition of Zr to the CoCe catalyst; thus, it is most suitable for use in high temperature WGSR.

Cu nanoparticles confined in TiO2 nanotubes to enhance the water-gas shift reaction activity

ABSTRACT It is of great significance to develop water-gas shift (WGS) catalyst with high catalytic activity in low-temperature operational regime. In this paper, we have prepared Cu confined in TiO2 nanotubes (TiO2NT, Cu-in-TiO2NT) catalyst via a vacuum-assisted impregnation method and subsequent calcination. The confined Cu-in-TiO2NT catalyst exhibits the higher CO conversion and H2 production rate than that of the Cu loaded on TiO2NT catalyst throughout the entire reaction temperature range. At the reaction temperature of 250°C and 300°C, the CO conversion of the confined catalyst is twofold and fourfold, respectively, higher than that of the supported catalyst, demonstrating superior catalytic activity toward WGS reaction. Due to the confinement effect of TiO2NT, the confined Cu-in-TiO2NT catalyst can enhance the concentration of the oxygen vacancies for H2O activation, contributing to the higher WGS activity.

Size effect-tuned water gas shift reaction activity and pathway on ceria supported platinum catalysts

The interfacial electronic and geometric effects behind the size effect are crucial in determining the catalytic performance of supported metal catalysts, whereas they remain still unknown for most of important heterogeneous catalytic reactions such as water-gas shift reaction (WGSR). In this work, we report a profound size effect in five Pt/CeO2 catalysts among Pt single atoms, sub-nanoclusters (ca. 0.8 nm) and nanoparticles (3.8–9.3 nm) for the WGSR. The catalyst with about 3.8 nm Pt nanoparticles had the highest activity, superior to the other four Pt/CeO2 catalysts. Ptδ+-OV-Ce3+ species served as the interfacial active sites, wherein the carboxyl pathway seemed more preferred than the formate route, and favored high activity. Such high activity and pathway preference are due to both of the electronic and geometric effects. On the one hand, the electronic metal-support interaction (EMSI) modulated by the metal deposit size tunes the activation of the CO adsorbed on Pt sites. On the other hand, the abundant interfacial oxygen vacancies for the geometric effect of providing the active sites to activate and dissociate H2O.

The Study of Reverse Water Gas Shift Reaction Activity over Different Interfaces: The Design of Cu-Plate ZnO Model Catalysts

CO2 hydrogenation to methanol is one of the main and valuable catalytic reactions applied on Cu/ZnO-based catalysts; the interface formed through Zn migration from ZnO support to the surface of Cu nanoparticle (ZnOx-Cu NP-ZnO) has been reported to account for methanol synthesis from CO2 hydrogenation. However, the accompanied reverse water gas shift (RWGS) reaction significantly decreases methanol selectivity and deactivates catalysts soon. Inhibition of RWGS is thus of great importance to afford high yield of methanol. The clear understanding of the reactivity of RWGS reaction on both the direct contact Cu-ZnO interface and ZnOx-Cu NP-ZnO interface is essential to reveal the low methanol selectivity in CO2 hydrogenation to methanol and look for efficient catalysts for RWGS reaction. Cu doped plate ZnO (ZnO:XCu) model catalysts were prepared through a hydrothermal method to simulate direct contact Cu-ZnO interface and plate ZnO supported 1 wt % Cu (1Cu/ZnO) catalyst was prepared by wet impregnation for comparison in RWGS reaction. Electron paramagnetic resonance (EPR), XRD, SEM, Raman, hydrogen temperature-programmed reduction (H2-TPR) and CO2 temperature-programmed desorption (CO2-TPD) were employed to characterize these catalysts. The characterization results confirmed that Cu incorporated into ZnO lattice and finally formed direct contact Cu-ZnO interface after H2 reduction. The catalytic performance revealed that direct contact Cu-ZnO interface displays inferior RWGS reaction reactivity at reaction temperature lower than 500 °C, compared with the ZnOx-Cu NP-ZnO interface; however, it is more stable at reaction temperature higher than 500 °C, enables ZnO:XCu model catalysts superior catalytic activity to that of 1Cu/ZnO. This finding will facilitate the designing of robust and efficient catalysts for both CO2 hydrogenation to methanol and RWGS reactions.

Process characteristics and mechanism of Na2CO3-catalyzed water-gas shift reaction in a benzene-containing hydrothermal system

Water-gas shift reaction (WGSR) is one of the most crucial reactions in the lignite-liquefaction system containing syngas (CO + H2) and H2O. In this study, the characteristics of WGSR were investigated in similar liquefaction systems, such as a benzene-containing hydrothermal system employing Na2CO3 as a catalyst. The CO conversion and productions of CO2 and H2 during WGSR in these systems of 20–60% water content were investigated at 350–450 °C. The results demonstrated that as the reaction temperature and water content increased, CO conversion increased, thereby resulting in enhanced WGSR. When benzene was added to the hydrothermal system, the activity of WGSR reduced evidently because of the inhibition effect of benzene. Moreover, when Na2CO3 was added to the benzene-containing hydrothermal system, the activity of WGSR was enhanced, indicating that Na2CO3 exerted a strong promoting effect on WGSR. Noticeably, in this benzene-containing hydrothermal system with Na2CO3 as the catalyst, the productions of H2 and CO2 were not equal to the consumption of CO during WGSR. This was due to the formation of intermediate products, such as NaHCO3, NaOH, HCOONa, and Na2C2O4. Based on the foregoing, the Na2CO3-catalyzed WGSR was accelerated via the ionic reactions of these intermediate products. Therefore, the mechanism of Na2CO3-catalyzed WGSR in a hydrothermal system with an organic solvent was developed, thereby affording an insight into the lignite-liquefaction technology in syngas and H2O systems.

Water-gas shift reaction catalyzed by Au32M6 (M = Cu, Pt, Pd, Rh, Ir) core-shell nanoclusters: A density functional theory study

In this paper, the mechanism of water-gas shift reaction (WGSR) on Au32M6 (M = Cu, Pt, Pd, Rh, Ir) core-shell nanoclusters was investigated by density functional theory (DFT). The result shows that the unique synergistic effect in the core-shell structure of Au32M6 has a significant effect on the activity of the catalyst. Compared with the Au38 nanocluster, in the case of Au32M6, the charge transfer between the M6 core and the Au32 shell is larger after the formation of the core-shell nanocluster. The calculation of the binding energy indicates that the Au32M6 core-shell nanoclusters is more stable than Au38 nanocluster. The parameters for the center of d-band show that d-orbital electrons of Au32Pd6 nanoclusters closer to the Fermi level than other nanoclusters, which indicates the Au32Pd6 nanocluster have better electron activity. In addition, we also found out the minimum energy pathways (MEP) of each nanocluster based on the adsorption investigation of various species on Au32M6 in the WGSR. The calculation results show that Au32Pd6 nanocluster exhibits excellent catalytic activity for WGSR, the reaction pathway was ER 1 → ER 4 → ER 5-b → ER 6.

Reducing gas atmosphere (H2, CO) assisted formation of Fe-Ce-Ox composite oxides with enhanced catalytic activity for water-gas shift reaction

Composite oxides of CeO2 nanorods and Fe2O3 nanoparticles were prepared by a reducing gas atmosphere (H2 or CO) assisted hydrothermal method and used for the water-gas shift reaction. Powder XRD, Raman and XPS analyses showed that Fe3+ was introduced into the lattice space of CeO2 crystal structure to a significantly extent in a reducing gas atmosphere, which resulted in an increase in the activity of the catalyst for the water-gas shift reaction. DFT calculations showed that water molecules are more strongly adsorbed on the surface of the Fe-Ce-Ox composite oxide, which favors the water-gas shift reaction. Consequently, gas reductive atmosphere synthesis is considered to be an effective means to increasing the doping effect and prepare high performance WGS reaction catalysts.