Pt/ZrO2 catalyst for a single-stage water-gas shift reaction: Ti addition effect

Ti modified Pt/ZrO₂ catalysts were prepared to improve the catalytic activity of Pt/ZrO₂ catalyst for a single-stage WGS reaction and the Ti addition effect on ZrO₂ was discussed based on its characterization and WGS reaction test. Ti impregnation into ZrO₂ increased the surface area of the support and the Pt dispersion. The reducibility of the catalyst was enhanced in the controlled Ti impregnation (∼20 wt.%) over Pt/ZrO₂ by the Pt-catalysed reduction of supports, particularly, at the interface between ZrO₂ and TiO₂. The significant CO₂ gas band in the DRIFTS results of Pt/Ti[20]/ZrO₂ indicated that the Ti addition made the formate decomposition rate faster than the Pt/ZrO₂ catalyst, linked with the enhanced Pt dispersion and reducibility of the catalyst. Consequently, Ti impregnation over the ZrO₂ support led to a remarkably enhanced CO conversion and the reaction rate of Pt/Ti[20]/ZrO₂ increased by a factor of about 3 from the bare Pt/ZrO₂ catalyst.     

Effect of precipitation sequence on physicochemical properties of CeO2 support for hydrogen production from low-temperature water-gas shift reaction

A one-step reverse precipitation method has been developed to prepare nano-sized ceria (CeO₂) support with controlled physicochemical properties for low temperature water-gas shift (LT-WGS) reaction. The nano-sized CeO₂ support prepared by reverse precipitation method has a high Brunauer-Emmett-Teller (BET) surface area of 162.8 m²/g. To compare catalytic activity with that of CeO₂ prepared by normal precipitation method, 5 wt% Cu was employed as the active metal, coupled to the CeO₂ support. The catalytic activity of CeO₂ supported Cu catalyst prepared by reverse precipitation method was evaluated for the first time in LT-WGS reaction. Notably, the CeO₂ – R supported Cu catalyst, prepared by reverse precipitation method, showed higher CO conversion and turnover frequency (TOF) values than CeO₂–N supported Cu catalyst prepared by normal precipitation method.     

Advanced nickel metal catalyst for water-gas shift reaction

A comparative study has been performed to investigate the effectiveness of a Ni metal catalyst before and after impregnation with potassium for the water-gas shift (WGS) reaction. The potassium-modified Ni metal is both more active and more selective for the WGS reaction than the unmodified Ni catalyst. Furthermore, there is no carbon deposition on the modified Ni catalyst. The amount of H₂ produced and the CO conversion via WGS over the potassium-modified Ni catalyst are higher than those for the commercial high-temperature shift (HTS) catalyst under severe experimental conditions (gas-hourly space velocity = 80 000 h⁻¹, CO 60% and H₂ 40%). The suppression of methanation over the modified Ni metal is attributed to the action of the incorporated potassium in increasing the density of the active hydroxyl group that takes part in the WGS reaction to form the intermediate.     

Hydrogen production by water-gas shift reaction over Co-promoted MoS2/Al2O3 catalyst: The intrinsic activities of Co-promoted and unprompted sites

Co-promoted MoS₂/Al₂O₃ is the industrial-widely used catalyst for hydrogen production by water-gas shift (WGS) reaction under sulfur-containing condition. Despite of the intensive physicochemical characterizations, the intrinsic activities of Co-promoted and unprompted sites on this catalyst are still unreported, mainly owning to the lack of quantification method of catalytic sulfide sites. With low temperature CO adsorption followed by IR spectroscopy, a distinguish technique developed by our group, this short communication reports the temperature-dependent TOFs (turnover frequencies) of these two sites, and reveals that Co-promoted site is intrinsically much more active than unprompted site at low temperatures, while these two sites are catalytically comparable at higher reaction temperatures. The catalytically different performances are related to the different apparent activation energies of WGS reaction on these two sites. This work fills in the long-standing gaps in hydrogen production by WGS reaction over sulfided CoMo/Al₂O₃ catalyst.     

Pt on SAS-CeO2 nanopowder as catalyst for the CO-WGS reaction

In this paper, we present a study on the preparation of ceria nanopowder by Supercritical Antisolvent technique and its use as catalysts support for water gas shift reaction. The effect of the concentration of ceria precursor and the solution flow rate was evaluated on particle size and granulometric distribution. The increase of concentration led to an increase in the average particle size, whereas the solution flow rate had a negligible effect. The platinum/ceria catalyst was prepared by wet impregnation and fully characterized; SEM and TEM-EDX showed a mean particle size of around 50 nm and a good dispersion of the active component. The results of the activity tests highlighted a good performance of the SAS-derived catalyst, that showed higher CO conversion with respect to a catalyst obtained from commercial ceria nanopowder.     

Hydrogen production via water-gas shift reaction over gold supported on Ni-based layered double hydroxides

Co-precipitated NiAl and NiMgAl layered double hydroxides (LDHs) were prepared at M²⁺/Al³⁺ molar ratio of 2.5/1 and subsequently promoted with gold targeting to be studied as catalysts and supports of gold particles in the hydrogen production via water-gas shift (WGS) reaction. Powder X-ray diffraction and N₂ physisorption before and after WGS tests were applied to investigate the impacts of Mg and Au on the structure and catalytic behavior of the systems. Partial replacement of Ni by Mg resulted in moderate activity of NiMgAl and Au/NiMgAl catalysts than NiAl analogues due to: (i) smaller Ni amount that could not supply sufficient number catalytically active sites; (ii) higher thermal stability leading to the creation of the active Ni species at higher temperatures, and (iii) partial regeneration of the layered structure with the assistance of small Au particles, Mg, and the reaction medium as well. Favorable role of gold on Au/NiAl WGS activity was elucidated.     

Effects of Pt precursors on Pt/CeO2 to water-gas shift (WGS) reaction activity with Langmuir-Hinshelwood model-based kinetics

The crystallite size effects of Pt nanoparticles on the CeO₂ (Pt/CeO₂) prepared with four different Pt precursors were investigated in terms of their thermal stability and catalytic activity for a water-gas shift (WGS) reaction using the compositions of reformates after a typical steam reforming of propane. The Pt/CeO₂ prepared with a diamine dinitroplatinum (Pt(NO₂)₂(NH₃)₃) precursor, which forms the cationic Pt(NH₃)₂²⁺ species on the negatively-charged CeO₂ surfaces, revealed a superior catalytic activity and thermal stability by forming the partially oxidized smaller Pt nanoparticles decorated with metallic Pt surfaces as well as by forming the strongly interacted PtOx-CeO₂ interfaces. The stable preservation of the pristine smaller Pt nanoparticles with small aggregations even under the hysteresis test from 250 to 400 °C was mainly attributed to the strong metal-support interactions. The optimized Pt/CeO₂ was further studied to obtain kinetic equations derived by Langmuir-Hinshelwood (LH) model, and the optimal operating conditions of WGS reaction were found to be ~280 °C and H₂O/CO molar ratio of 9 with the activation energy of ~78.4 kJ/mol.     

Nanofiber structured oxygen defective CoFe2O4-x catalyst for the water-gas shift reaction in waste-to-hydrogen processes

Waste-to-hydrogen processes are a way to produce hydrogen from waste and reduce the amount of landfill/incineration of wastes simultaneously through the gasification of waste. The water-gas shift (WGS) reaction is a key step in this waste-to-hydrogen process by removing the CO and producing additional H₂. A nanofiber-structured CoFe₂O₄ catalyst was synthesized by the electrospinning method, and the catalytic performance in WGS using waste-derived synthesis gas was compared with that of catalysts prepared by sol-gel, hydrothermal, and co-precipitation methods. The CoFe₂O₄ catalyst synthesized by the electrospinning method showed a clear nanofiber structure and revealed a superior redox property. This superior redox property, which has a large relation with the high oxygen storage capacity of the catalyst, induced the formation of an active phase (Co⁰ and Fe₃O₄) in CoFe₂O₄. As a result, the nanofiber structured oxygen defective CoFe₂O_4-x prepared by the electrospinning method showed the best catalytic activity in this study.     

Enhanced water-gas shift reaction performance of MOF-derived Cu/CeO2 catalysts for hydrogen purification

The water-gas shift (WGS) reaction has received renewed interest because it is one of the key reactions for producing hydrogen and renewable energy in contemporary technologies like fuel cells and bio-refineries. Catalysts play an important role in WGS reaction for achieving high CO conversion and hydrogen generation activity. Thus, the performance and stability of catalysts are vital for the WGS reaction. In the present work, the CuCe metal-organic framework (MOF) is used as a template to derive the nanostructured Cu/CeO₂ catalyst. The influence of CuCe-MOF templated approach on the WGS activity of Cu/CeO₂ has been established. Different Cu doping levels had a significant impact on WGS activity. Amongst, the Ce_0.8Cu_0.2O₂ (Cu2Ce) catalyst had a highest CO conversion (96%). The long-term stability tests further prove that the Cu2Ce catalyst had maintained high CO conversion over 100 h reaction time. XRD and TEM results suggest that different loadings of Cu content have a distinct impact on the dispersion of Cu and the catalytic properties. N₂O chemisorption results suggest that 20 wt.% of Cu loading resulted in high Cu dispersion (52%) compared to other loadings. The H₂-temperature programmed reduction (TPR) revealed that the superior catalytic activity of Cu2Ce catalyst could be attributed to the strong reducibility (i.e. lower redox temperature) derived from CuCe-MOF template. It further suggests well-dispersed copper oxide species at low Cu loadings and crystalline copper oxide species at high Cu loadings. This work emphasizes the significance of Cu/CeO₂ catalysts with exceptional catalytic activity and stability for the WGS process with MOF-precursor.     

Preparation of highly dispersed Cu/SiO2 doped with CeO2 and its application for high temperature water gas shift reaction

Highly dispersed Cu/SiO₂ catalysts doped with CeO₂ have been successfully prepared via in-situ self-assembled core-shell precursor route. The prepared catalysts were characterized by XRD, SEM, TPR, chemisorption and XPS techniques. The results showed that our newly developed method could not only prepare highly dispersed supported metal catalysts but also highly dispersed supported CeO₂ on silica. The highly dispersed CeO₂ showed strong interaction with highly dispersed Cu. The synergy between the highly dispersed CeO₂ and the highly dispersed Cu exhibited high catalytic activity for high temperature water gas shift reaction compared to the catalysts prepared with the routine method of incipient impregnation.     

Water-gas shift reaction over CuO/CeO2 catalysts: Effect of CeO2 supports previously prepared by precipitation with different precipitants

A series of CeO₂ supports were firstly prepared by precipitation method with NH₃⋅H₂O (NH), (NH₄)₂CO₃ (NC) and K₂CO₃ (KC) as precipitant, respectively, and then CuO/CeO₂ catalysts were fabricated by depositing CuO on the as-obtained CeO₂ supports by deposition-precipitation method. The effect of CeO₂ supports prepared from different precipitants on the catalytic performance, physical and chemical properties of CuO/CeO₂ catalysts was investigated with the aid of XRD, N₂-physisorption, N₂O chemisorption, FT-IR, TG, H₂-TPR, CO₂-TPD and cyclic voltammetry (CV) characterizations. The CuO/CeO₂ catalysts were examined with respect to their catalytic performance for the water-gas shift reaction, and their catalytic activities and stabilities are ranked as: CuO/CeO₂-NH > CuO/CeO₂-NC > CuO/CeO₂-KC. Correlating to the characteristic results, it is found that the CeO₂ support prepared by precipitation with NH₃⋅H₂O as precipitant (i.e., CeO₂-NH-300) has the best thermal stability and least surface “carbonate-like” species, which make the corresponding CuO/CeO₂-NH catalyst presents the highest Cu-dispersion, the highest microstrain (i.e., the highest surface energy) of CuO, the strongest reducibility and the weakest basicity. While, the precipitants that contain CO₃^2- (e.g. (NH₄)₂CO₃ and K₂CO₃) result in more surface “carbonate-like” species of CeO₂ supports and CuO/CeO₂ catalysts. As a result, CuO/CeO₂-NC and CuO/CeO₂-KC catalysts present poor catalytic performance.     

Water-gas shift reaction over magnesia-modified Pt/CeO2 catalysts

Fuel cells have risen as a clean technology for power generation and much effort has been done for converting renewable feedstock in hydrogen. The water-gas shift reaction (WGS) can be applied aiming at reducing the CO concentration in the reformate. As Pt/CeO₂ catalysts have been pointed out as an alternative to the industrial WGS catalysts, the modification of such systems with magnesium was investigated in this work. It was shown that the addition of MgO to Pt/CeO₂ increased the activity and stability of the catalyst irrespective of the preparation method used, either impregnation or co-precipitation. Based on TPR and IR spectroscopy experiments, it was seen that the presence of magnesium improved ceria reduction favoring the creation of OH groups, which are considered the active sites for the WGS reaction. The evolution of the surface species formed under reaction conditions (CO, H₂O, H₂) observed by DRIFTS evidenced that the formation of formate species and the generation of CO₂ is closely attached to each other; under a reaction stream containing hydrogen the presence of formate species showed to be more relevant while the CO₂ formation was hindered. It is suggested that the addition of MgO favors the formate decomposition and lower the carbonate concentration on the catalyst surface during WGS reaction.     

The application of MOF-derived CeO2 to synthesize the Cu/CeO2 catalyst for the hydrogen production via water gas shift reaction

The development of catalysts for the water-gas shift (WGS) reaction is attracting attention because of the increased interest in on-site small-scale hydrogen production, which requires highly active and stable catalytic performance under severe conditions. In this study, metal–organic frameworks (MOF), which have been adopted in various fields because of their high surface area, diversity of assemblies, and uniform porosity, were applied to prepare Cu/CeO₂ catalysts for the WGS reaction. MOF-derived CeO₂ (MDC) was obtained from a Ce-BTC-based MOF calcined at different temperatures. Various techniques were used to investigate the physicochemical properties of the Cu/MDC catalysts. Important properties that determine the catalytic performance, such as crystallinity, surface area, Cu dispersion, reducibility, and oxygen storage capacity (OSC), were affected by the treatment temperature of MDC. Among the Cu/MDC catalysts, Cu/MDC prepared with MDC that was treated at 400 °C (Cu/MDC(400)) exhibited the highest CO conversion at reaction temperatures of 200–400 °C. In addition, Cu/MDC(400) maintained 80% of its initial CO conversion after 48 h on stream, even at a very high gas hourly specific velocity of 50,233 mL·g_cat⁻¹·h⁻¹. This result was attributed to the high surface area, Cu dispersion, OSC, and easier reducibility of the Cu/MDC(400) catalyst compared to Cu supported on MDC calcined at other temperatures.     

CeO2 overlapped with nitrogen-doped carbon layer anchoring Pt nanoparticles as an efficient electrocatalyst towards oxygen reduction reaction

To engineering high-efficient, sustainable and novel Pt-based composite system, a newly “Pt-oxide” based composites electrocatalyst of “CeO₂ overlapped with nitrogen-doped carbon layer anchoring Pt nanoparticles” (PtCeO₂@CN) has been fabricated. In comparison with Pt/C, the results exhibit that PtCeO₂@CN possesses a preferable methanol tolerance ability, superior stability (30000 s degradation: 35% for PtCeO₂@CN vs. 50% for Pt/C), and more positively the onset potential (16 mV) as well as half-wave potential (29 mV) towards oxygen reduction reaction. Further, the investigation shows that PtCeO₂@CN has a certain selectivity with quasi-four electron pathway (n = 3.2–3.3 e^?). This is attributed to the establishment of “nitrogen-doped carbon layer” structure, which heightens the conductivity of CeO₂, further promotes electron transfer between Pt and CeO₂, as well as strengthens the anchoring effect for Pt nanoparticles. Overall, this study would shed bright light to develop some effective Pt-oxide based composite electrocatalysts.     

Modeling and simulation of water-gas shift in a heat exchange integrated microchannel converter

The aim of this study is to analyze the operation of a heat exchange integrated, Pt-CeO₂/Al₂O₃ washcoated microchannel water-gas shift (WGS) reactor under fuel processing conditions by mathematical modeling techniques. In this context, operation of a single microchannel is modeled, whose outcomes are compared with experimental data obtained from the literature. Simulations show good agreement with the experimental data, with an error below 4%. Upon its validation, single channel model is used to simulate a heat exchange integrated microchannel reactor, which involves periodically located groups of reaction and air-fed cooling channels. The integrated reactor is modeled by 2D Navier-Stokes equations together with reactive transport of heat and mass. Incorporation of heat exchange function minimizes the impact of thermodynamic limitations on WGS by precise regulation of reaction temperature and gives 77.6% CO conversion, which is 67.4% in the absence of cooling. Improvement in conversion from 69.2% to 77.6% is observed upon increasing feed temperature of the reaction stream from 565 to 595 K, above which the reaction is controlled by equilibrium. Coolant feed temperature, however, changes conversion only by <1%. Isothermal conditions are obtained upon feeding reaction and coolant channels at 595 K and 587 K, respectively. Changes in the thickness and material of the wall between the channels give limited deviations in conversion. An integrated reactor with 2.37 L volume is sufficient for supplying H₂ necessary to drive a 1 kW PEMFC unit.     

Inhibition of water-gas shift reaction activity of oxide-supported Pt catalyst by H2 and CO2

A catalyst composed of platinum-group metals supported on an oxide exhibits high activity in a low-temperature water-gas shift (LT-WGS) reaction; however, the reaction rate is greatly reduced when H₂ or CO₂, the product gases of the WGS reaction, are included in the reactant stream. In this study, we attempted to understand the origin of this activity inhibition by analyzing the kinetic data with in-situ CO-diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The WGS reaction rate decreases more severely by H₂ than CO₂. The CO-DRIFTS spectra indicate that this can be explained by H₂ preoccupying the active sites for the WGS reaction. In addition, by comparing the kinetic data with the literature, it could be inferred that a similar inhibition mechanism is operating in other oxide-supported Pt catalysts. Considering this inhibition mechanism will be important for the development of catalysts with high WGS activity in reformate gas.     

High pressure palladium membrane reactor for the high temperature water-gas shift reaction

The water-gas shift (WGS) catalytic membrane reactor (CMR) incorporating a composite Pd-membrane and operating at elevated temperatures and pressures can greatly contribute to the efficiency enhancement of several methods of H₂ production and green power generation. To this end, mixed gas permeation experiments and WGS CMR experiments have been conducted with a porous Inconel supported, electroless plated Pd-membrane to better understand the functioning and capabilities of those processes. Binary mixtures of H₂/He, H₂/CO₂, and a ternary mixture of H₂, CO₂ and CO were separated by the composite membrane at 350, 400, and 450 °C, 14.4 bar (P_tube = 1 bar), and space velocities up to 45,000 h⁻¹. H₂ permeation inhibition caused by reversible surface binding was observed due to the presence of both CO and CO₂ in the mixtures and membrane inhibition coefficients were estimated. Furthermore, WGS CMR experiments were conducted with a CO and steam feed at 14.4 bar (P_tube = 1 bar), H₂O/CO ratios of 1.1-2.6, and GHSVs of up to 2900 h⁻¹, considering the effect of the H₂O/CO ratio as well as temperature on the reactor performance. Experiments were also conducted with a simulated syngas feed at 14.0 bar (P_tube  = 1 bar), and 400-450 °C, assessing the effect of the space velocity on the reactor performance. A maximum CO conversion of 98.2% was achieved with a H₂ recovery of 81.2% at 450 °C. An optimal operating temperature for high CO conversion was identified at approximately 450 °C, and high CO conversion and H₂ recovery were achieved at 450 °C with high throughput, made possible by the 14.4 bar reaction pressure.     

Kinetics of the water-gas shift reaction over a La0.7Ce0.2FeO3 perovskite-like catalyst using simulated coal-derived syngas at high temperature

The kinetics of the water-gas shift (WGS) reaction over a novel La_0.7Ce_0.2FeO₃ perovskite-like catalyst is investigated using simulated coal-derived syngas at temperatures of 550 °C and 600 °C which are higher than the maximum operating temperature limit for conventional high temperature WGS catalysts. The influences of CO, CO₂, H₂O and H₂ concentration on WGS reaction rate are determined using selected gas compositions that might be encountered in a coal-based gasification system. An empirical power-law rate model used in this study is found to correlate well with experimental data with good accuracy. Kinetics parameters over La_0.7Ce_0.2FeO₃ obtained in this study are mostly in agreement with those previously measured using Fe-Cr based commercial catalysts in a range of relatively lower temperatures (300-500 °C).     

Effect of process variables on Pt/CeO2 catalyst behaviour for the PROX reaction

A Pt/CeO₂ catalyst has been evaluated for CO oxidation, both in the absence of H₂ and in H₂-rich feedstreams. The catalyst shows high activity and selectivity at temperatures as low as 80 °C, what makes it a viable catalyst for the selective depletion of CO in the temperature range at which PEMFC operate. The effect of: oxygen excess during operation (λ)$(\lambda )$, the presence of either CO₂ (5%), H₂O (5%) or both in the feedstream, and the spatial time, on catalyst activity and selectivity has been evaluated.