Low-temperature water–gas shift reaction over supported Cu catalysts

The low-temperature water–gas shift (WGS) reaction has been carried out at a very high gas hourly space velocity (GHSV) of 36,201 h⁻¹ over supported Cu catalysts prepared by an incipient wetness impregnation method. The preparation method was optimized to get a highly active CeO₂ supported Cu catalyst for low-temperature WGS. Co-precipitated Cu–CeO₂ exhibited excellent catalytic performance as well as 100% CO₂ selectivity. The high activity and stability of co-precipitated Cu–CeO₂ catalyst is correlated to its easier reducibility, high surface area and the nano-sized CeO₂ with CuO species interacting with the support.     

Influence of coexisting Al2O3 on the activity of copper catalyst for water–gas-shift reaction

Influence of coexisting Al₂O₃ on the catalytic activity for low-temperature water–gas-shift (LT-WGS) reaction over Cu catalyst was investigated. The catalytic activity of Cu/Al₂O₃ catalyst increased with decreasing mesopore size when S/C ratio was 2.2, whereas the catalytic activity with S/C ratio = 4.6 increased with increasing mesopore size. IR measurement combined with kinetic study suggested that the low catalytic activity of Cu/CeO₂ catalyst comes from the restriction of CO adsorption on Cu⁰ by bidentate-type carbonate formed on the strong basic site of CeO₂ support. On the other hand, it was found that bidentate-type carbonate was not formed on Cu/Al₂O₃ showing high catalytic activity for LT-WGS reaction.     

Methanation of carbon dioxide over Ni/CeO2 catalysts: Effects of support CeO2 structure

The CeO₂, which were prepared by hard-template method, soft-template method, and precipitation method, were used as support to prepare Ni/CeO₂ catalysts (named as NCT, NCS, and NCP catalysts, respectively). The prepared catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and Brunauer–Emmett–Teller (BET). Hydrogen temperature-programmed reduction (H₂-TPR) was also used to study the reducibility of the support nickel precursors. Moreover, CO₂ catalytic hydrogenation methanation was used to investigate the catalytic properties of the prepared NCT, NCS, and NCP catalysts. H₂-TPR and XRD results showed that the NiO can be reduced by H₂ to produce metal Ni species, and the surface oxygen species existing on the surface of the support CeO₂ can also be reduced by H₂ to form surface oxygen vacancies. Low-angle XRD, TEM, and BET results indicated that the NCT and NCS catalysts had developed mesoporous structure and high specific surface area of 104.7 m² g^?1 and 53.6 m² g^?1, respectively. The NCT catalyst had the highest CO₂ methanation activity among the studied NCT, NCS, and NCP catalysts. The CO₂ conversion and CH₄ selectivity of the NCT catalyst can reach 91.1% and 100% at 360 °C and atmospheric pressure. The NCP catalyst, which had low specific surface area and low porosity, performed less CO₂ conversion and higher CH₄ selectivity than the NCT and NCS catalysts till 400 °C.     

CO2 hydrogenation over differently morphological CeO2‐supported Cu‐Ni catalysts

Differently morphological CeO₂‐supported Cu‐Ni catalysts utilized for carbon dioxide hydrogenation to methanol were prepared by the method of impregnation. The 100‐ to 300‐nm CeO₂ nanorod‐supported catalyst dominantly exposed low‐energy (100) and (110) facets, and the Cu‐Ni supported on 10‐ to 20‐nm CeO₂ nanospheres and on irregular CeO₂ nanoparticles were both enclosed by (111) facets owning high energy. Besides, all CeO₂‐supported Cu‐Ni catalysts possess oxygen vacancies, which can active and absorb CO₂ and is further beneficial for the reaction. Most oxygen vacancies were generated from the Ce⁴⁺ reduction to Ce³⁺ with the ceria lattice cell expansion, and small amount of oxygen vacancies resulted from the Ce⁴⁺ replacement by Cu or/and Ni atom. Because of the exposed (100) and (110) facets and numerous oxygen vacancies, well‐defined CeO₂ nanorod‐supported Cu‐Ni alloy showed more superior catalytic performance than on CeO₂ nanospheres and nanoparticles.     

Morphology effect of ceria on the performance of CuO/CeO2 catalysts for hydrogen production by methanol steam reforming

Nano-rod(R), nano-particle(P) and sponginess(S) of ceria samples were used to study catalytic performance of hydrogen production by methanol steam reforming. The samples were prepared by hydrothermal method, precipitation method, and sol-gel method, respectively, and the CuO was supported on the different morpholopy of CeO₂ samples by wet impregnation. SEM, TEM, XRD, XRF, BET, H₂-TPR, XPS and N₂O titration methods were used to study correlation between the structure and the catalytic performance for methanol steam reforming. The results showed that the morphology of the prepared CeO₂ support dramatically influenced the performance of catalysts. Due to the stronger interaction between copper oxide and ceria support, the CuO/CeO₂-R catalyst had exhibited the better catalytic activity than those of the CuO/CeO₂P and CuO/CeO₂S catalysts. Moreover, higher Cu dispersion, lower reduction temperature of CuO, and higher content of active species Cu⁺ were also advantageous to raising catalytic effects. Besides, with the highest content of surface Ce³⁺, the CuO/CeO₂-R had estimated the content of oxygen vacancy on the surface of the catalyst. The existence of surface oxygen vacancy had a positive effect on the methanol steam reforming.     

The effect of barium-promoted for microsphere Ru/CeO2 catalysts in ammonia synthesis

In this essay, the effect of the morphology of the CeO₂ support and the Ba promoter on the ammonia synthesis reaction was studied. CeO₂ support with {110} and {100} crystal planes and more oxygen vacancies enhanced the catalytic activity of ammonia synthesis. The relatively uniform microspheres structure CeO₂ support (CeO₂-MS) with {110} and {100} crystal planes was synthesized. The structural functions of the as-synthesized CeO₂ support for the Ru-based catalyst were investigated in the ammonia synthesis reaction. The results of catalytic performance showed that the catalytic activity of 2.5%Ru/CeO₂-MS catalyst reached 8940 μmol· g^?1· h^?1 at 450 ℃, 3.8 MPa, H₂/N₂ = 3 (60 mL?min^?1), which is higher nearly 2.5 times than the 2.5%Ru/CeO₂-commercial (CeO₂-C). And the catalytic activity of catalysts increased with the increase of reaction temperature. The activity of 6%Ba-2.5%Ru/CeO₂-MS (24000 μmol· g^?1· h^?1) catalyst increased about 268% than that of catalyst without addition of Ba. Their physical and chemical properties were characterized by XRD, BET, HRTEM, H₂-TPR, H₂-TPD, and XPS analyses. Our results indicate that the 2.5%Ru/CeO₂-MS catalyst and catalysts involving promoters (Cs, K, and Ba) exhibit significant support-morphology-dependent catalytic activity for ammonia synthesis.     

Supported mesoporous Cu/CeO2-δ catalyst for CO2 reverse water–gas shift reaction to syngas

The design and development of a high performance hydrogenation catalyst is an important challenge in the utilization of CO₂ as resources. The catalytic performances of the supported catalyst can be effectively improved through the interaction between the active components and the support materials. The obtained results demonstrated that the oxygen vacancies and active Cu⁰ species as active sites can be formed in the Cu/CeO_2-δ catalysts by the H₂ reduction at 400 °C. The synergistic effect of the surface oxygen vacancies and active Cu⁰ species, and Cu⁰–CeO_2-δ interface structure enhanced catalytic activity of the supported xCu/CeO_2-δ catalysts. The electronic effect between Cu and Ce species boosted the adsorption and activation performances of the reactant CO₂ and H₂ molecules on the corresponding Cu/CeO_2-δ catalyst. The Cu/CeO_2-δ catalyst with the Cu loading of 8.0 wt% exhibited the highest CO₂ conversion rate in the RWGS reaction, reaching 1.38 mmol·g_cat⁻¹ min⁻¹ at 400 °C. Its excellent catalytic performance in the RWGS reaction was related to the complete synergistic interaction between the active species via Ce³⁺-□-Cu⁰ (□: oxygen vacancy). The Cu/CeO_2-δ composite material is a superior catalyst for the RWGS reaction because of its high CO₂ conversion and 100% CO selectivity.     

Achievement of hydrogen production from autothermal steam reforming of methanol over Cu-loaded mesoporous CeO2 and Cu-loaded mesoporous CeO2–ZrO2 catalysts

Hydrogen production by oxidative steam reforming of methanol (OSRM) or autothermal steam reforming of methanol (ASRM) was investigated over Cu-loaded mesoporous CeO₂ and Cu-loaded mesoporous CeO₂–ZrO₂ catalysts, synthesized via a nanocasting process using MCM-48 as a hard template, followed by a deposition–precipitation technique. Various Cu contents were loaded on the mesoporous CeO₂ and CeO₂–ZrO₂ supports. The fresh and spent catalysts were characterized by N₂ adsorption–desorption, X-ray diffraction, temperature-programmed oxidation, and X-ray photoelectron spectroscopy. The ASRM results showed that 9 wt% Cu loading onto mesoporous CeO₂ and CeO₂–ZrO₂ provided the best catalytic performance with 100% methanol conversion and 60% H₂ yield at 350° and 300 °C, respectively. Furthermore, the time-on-stream stability testing of the 9 wt% Cu loading catalyst was at 168 h, and the CO selectivity of these two catalysts indicated that the addition of ZrO₂ into the catalyst reduced the CO selectivity during the ASRM process.     

Enhanced performance of DMFC prepared by 10Cu/CeO2 catalyst and nanocomposite SPVA membranes with layer-by-layer coating of polyacrylic acid and chitosan

In the present study, TiO₂ nanoparticles are used as inorganic nanofiller material to prepare nanocomposite proton exchange membrane (PEM). Sulfonated polyvinyl alcohol (SPVA) is synthesized by 4-formylbenzene-1,3-disulfonic acid disodium salt hydrate and water. The cross-linking reaction is performed by glutaraldehyde. These membranes were then dip coated with polyacrylic acid and chitosan alternately and one layer-by-layer (LBL), two LBL and three LBL membranes were prepared. The chemical structure evaluation of SPVA membrane is performed using FTIR. The direct methanol fuel cell (DMFC) catalysts of 10Cu/CeO₂ and 10 Pt-10 CeO₂/C were prepared by reduction reaction and hydrothermal technique. Thus obtained material was spin coated on 2 × 2 cm² carbon paper to prepare catalyst anode/cathode. The morphology, size, and purity of catalyst particles are analysed by SEM, UV–visible spectroscopy, FTIR and EDS. Electrochemical analysis is also done to test the performance. Results show that Cu/CeO₂ catalyst shows excellent catalysis towards methanol oxidation, which is better than 10 Pt-10 CeO₂/C particles. The 10Cu/CeO₂ catalyst gives peak voltage of 915 mV for infinite resistance, which is higher than the reported value of the conventional 20 Pt/C catalyst (810 mV).     

The alcohol-modified CuZnAl hydroxycarbonate synthesis as a convenient preparation route of high activity Cu/ZnO/Al2O3 catalysts for WGS

The influence of the hydroxycarbonate precursors precipitation environment on the physico-chemical properties and catalytic activity in low-temperature water-gas shift (LT-WGS) reaction of Cu/ZnO/Al₂O₃ system has been studied. With the use of co-precipitation three precursors were obtained, which differed in the reactive medium, i.e. the solvent composition. Water, glycol aqueous solution or ethanol aqueous solution were used as the reactive medium. The prepared materials were characterized by means of XRF, XRD, BET, TG/MS, TPR, N₂O titration techniques as well as SEM method and their catalytic activity was compared in LT-WGS reaction in the kinetic regime and differential conditions. It was shown that Cu/ZnO/Al₂O₃ system of higher activity can be obtained by means of alcohol-assisted technique rather than using a conventional method. Precursor synthesis performed in ethanol aqueous solution contributes to obtaining highly active and stable catalysts.     

Combustion synthesis of copper ceria solid solution for CO2 conversion to CO via reverse water gas shift reaction

The reverse water–gas shift chemical (RWGS) reaction is a promising technique of converting CO₂ to CO at low operating temperatures, with high CO selectivity and negligible side products. In this study, we investigate the synthesis of Cu/CeO₂ catalyst using Solution Combustion Synthesis (SCS) technique and its performance for the RWGS reaction using a tubular packed bed reactor. Results indicate that the catalytic activity and stability of CeO₂ at low and moderate temperatures can be effectively improved by the addition of a small quantity of copper (1 wt%). The conversion of CO₂ improves with an increase in temperature, with a maximum value of 70% at 600 °C, showing a steady time on stream (TOS) performance for 1200 min with negligible carbon deposition of <0.05 wt%. The high catalyst activity is due to the synergistic interaction between the active Cu⁰ species and Ce³⁺-oxygen vacancy. The Cu/CeO₂ catalyst was also found to have 100% selectivity for CO, and no CH₄ was detected in the outlet stream. Moreover, the morphological characteristics of the support and catalysts (fresh and post-reaction samples), as well as the impact of reaction on the catalysts surface were investigated using various methods such as x-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy with energy dispersive x-ray spectra (SEM/EDX). The results demonstrate that Cu/CeO₂ offers a good potential for being a robust RWGS catalyst with exclusive selectivity for CO without the undesired methanation side-reaction.     

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.     

Hydrogen production from low temperature WGS reaction on co-precipitated Cu–CeO2 catalysts: An optimization of Cu loading

Low temperature water–gas shift (WGS) reaction has been carried out at the gas hourly space velocity of 72,152 h⁻¹ over Cu–CeO₂ catalyst prepared by a co-precipitation method. Cu loading was optimized to obtain highly active co-precipitated Cu–CeO₂ catalysts for low temperature WGS. 80 wt% Cu–CeO₂ exhibited the highest CO conversion as well as the most stable activity (X_CO > 46% at 240 °C for 100 h). The excellent catalytic performance is mainly due to a strong metal to support interaction, resulting in the prevention of Cu sintering.     

Copper catalysts prepared via microwave-heated polyol process for preferential oxidation of CO in H2-rich streams

The purposes of this study were to prepare a copper catalyst by the microwave-heated polyol (MP) process and subsequently to evaluate the feasibility of the preferential oxidation of CO (CO-PROX) in excess H₂. A CeO₂-TD support was firstly prepared by the thermal decomposition from Ce(NO₃)₃·6H₂O precursor. For comparison, commercial ceria (CeO₂-C) and activated carbon (AC) selected as support materials. Experimental results of CO-PROX indicated that the highest catalytic activity is achieved when the Cu/CeO₂-TD used as catalysts. Correlating to the characteristic results, it is found that the CeO₂-TD support prepared by the thermal decomposition has a large surface area and high mesoporosity; these properties contribute to the easy adsorption of pollutants and the effective dispersion of metal particles. Further investigation of feed composition found that Cu/CeO₂-TD catalysts possess 100% CO conversion even existence of CO₂ and H₂O in H₂-rich streams at 150 °C. Besides, a decrease in CO conversion was clearly observed above 175 °C for Cu/CeO₂-TD catalysts due to the reverse water gas shift reaction tending to reform CO from CO₂ and H₂.     

CeO2–ZrO2-promoted CuO/ZnO catalyst for methanol steam reforming

The Cu-based catalysts with different supports (CeO₂, ZrO₂ and CeO₂–ZrO₂) for methanol steam reforming (MSR) were prepared by a co-precipitation procedure, and the effect of different supports was investigated. The catalysts were characterized by means of N₂ adsorption–desorption, X-ray diffraction, temperature-programmed reduction, oxygen storage capacity and N₂O titration. The results showed that the Cu dispersion, reducibility of catalysts and oxygen storage capacity evidently influenced the catalytic activity and CO selectivity. The introduction of ZrO₂ into the catalyst improved the Cu dispersion and catalyst reducibility, while the addition of CeO₂ mainly increased oxygen storage capacity. It was noticed that the CeO₂–ZrO₂-containing catalyst showed the best performance with lower CO concentration, which was due to the high Cu dispersion and well oxygen storage capacity. Further investigation illuminated that the formation of CO on CuO/ZnO/CeO₂–ZrO₂ catalyst mainly due to the reverse water gas shift. In addition, the CuO/ZnO/CeO₂–ZrO₂ catalyst also had excellent reforming performance with no deactivation during 360 h run time and was used successfully in a mini reformer. The maximum hydrogen production rate in the mini reformer reached to 162.8 dm³/h, which can produce 160–270 W electric energy power by different kinds of fuel cells.     

Ce promoting effect on the activity and coke formation of Ni catalysts supported on mesoporous nanocrystalline γ-Al2O3 in autothermal reforming of methane

In this study methane autothermal reforming (ATR) was investigated over Ni/Al₂O₃ and Ni/Al₂O₃–CeO₂ catalysts. The catalyst carriers were prepared through a facile one-step method, which produced mesoporous nanocrystalline carriers for Ni catalysts. The samples were characterized by XRD, TPR, BET, TPO and SEM characterization techniques and the catalytic activity and stability were also studied at different conditions (GHSV and feed ratio) in methane ATR. It was found that the nickel catalyst supported on 3 wt.% Ce–Al₂O₃ exhibited higher activity compared to the catalysts supported on the Al₂O₃ and promoted Al₂O₃ with 1 and 6 wt.% Ce. The results also showed that the nickel catalyst supported on 3 wt.% Ce–Al₂O₃ possessed the highest resistance against carbon deposition in ATR reaction.     

High jolt-resistance monolithic CuO–CeO2/AlOOH/Al-fiber catalyst for CO-PROX: Influence of AlOOH/Al-fiber calcination on Cu–Ce interaction

Micro-reactors for the preferential oxidation of CO in H₂-rich stream (CO-PROX) are attractive for PEMFCs employed in portable electronic devices and automobiles, but the jolt is inevitable, which makes micro-reactors necessitate high jolt resistance. The monolithic structured catalyst could effectively resolve these problems. Herein, we employed the thin-felt monolithic Al-fiber substrate to fabricate the CuO–CeO₂/AlOOH/Al-fiber catalyst for the CO-PROX reaction. This catalyst was prepared via first growing AlOOH nanosheets onto the Al-fiber surface by steam oxidation method, followed by depositing CuO–CeO₂ onto the AlOOH/Al-fiber support. The preferred catalyst delivered 100% CO conversion and 81% O₂ selectivity at 140 °C with a gas hourly space velocity of 12,000 mL g^?1 h^?1, and particularly, performed stably for 120 h at the changeable temperatures of 120–160 °C. This work provides a strategy to tailor a qualified monolithic catalyst that couples the promising jolt resistance and catalytic performance at 120–160 °C.     

Effect of rare earth (RE – La,Pr, Nd) metal-doped ceria nanoparticles on catalytic hydrogen iodide decomposition for hydrogen production

In this work, high surface area rare earth (RE = La, Pr, and Nd) metal-doped ceria (CeO₂) nanocatalysts have been synthesized by the citric-aided sol-gel method for hydrogen-iodide decomposition in thermochemical water-splitting sulfur-iodine (SI) cycle for hydrogen production. This sol-gel method allows the insertion of rare earth metal M³⁺ ions into the CeO₂ material. Incorporation of rare earth metals created a different synergistic effect between RE and Ce components such as increase of oxygen mobility, oxygen vacancy, and thermal stability of the CeO₂ material. These doped-CeO₂ materials were characterized by various physicochemical techniques, namely, XRD, BET, ICP-AES, TEM, TGA, and RAMAN spectroscopy. XRD and TEM studies revealed 5–10 nm particles of the RE-CeO₂ material. Shifting of peaks and increase in lattice parameter values confirmed the formation of Ce-RE solid solutions (XRD and Raman). Incorporation of dopants resulted in an increase in the specific surface area (BET), thermal stability (TGA), and oxygen vacancy concentration (Raman). Among different dopants, CeO₂-L (La-doped CeO₂) material exhibits the highest specific surface area, thermal stability, and oxygen vacancy concentration, and smallest crystallite size. The catalytic activity of doped-CeO₂ materials is explored for hydrogen-iodide decomposition. The order of catalytic activity is as follows: CeO₂ < CeO₂-N (N = Nd) < CeO₂-P (P = Pr) < CeO₂-L (L = La). CeO₂-L shows higher catalytic activity and stability in comparison to the pure CeO₂ material. It also showed an excellent time-on-stream stability for 35 h. The apparent activation energy of CeO₂-L, CeO₂-P, and CeO₂-N was found to be 48.9, 54.8, and 61.4 kJ mol^?1, respectively. The effect of iodine on hydrogen iodide conversion was also studied over a CeO₂-L catalyst. Thus, RE-doped CeO₂ catalysts show a lot of potential of generating hydrogen from hydrogen iodide in the SI cycle.     

Promoted the reduction of Cu2+ to enhance CuOCeO2 catalysts for CO preferential oxidation in H2-rich streams: Effects of preparation methods and copper precursors

A series of CuOCeO₂ catalyst samples synthesized by using various methods (CuCe-SF-N, CuCe-UGC-N, CuCe-SG-N and CuCe-ST-N) and copper precursors (CuCe-SF-N, CuCe-SF-C, CuCe-SF-A and CuCe-SF-S) were estimated for CO preferential oxidation in H₂-rich streams. It was found that both synthesis routes and copper precursors have an important effect on catalytic behaviors of CuOCeO₂ catalyst. Compared to CuCe-UGC-N, CuCe-SG-N and CuCe-ST-N, CuCe-SF-N exhibits the lowest temperature and the widest temperature window for 100% CO conversion (about 50 °C), which should be attributed to synergistic effects of smaller crystallite size, the formation of more Cu⁺ species together with the high ratio of Ce³⁺/(Ce³⁺+Ce⁴⁺). Among the four catalysts prepared with different Cu precursors (CuCe-SF-N, CuCe-SF-C, CuCe-SF-A and CuCe-SF-S), the corresponding CO conversions of them are in the order of CuCe-SF-N > CuCe-SF-A > CuCe-SF-C » CuCe-SF-S. The lowest catalytic activity of CuCe-SF-S should be due to the presence of SO₄^2? species covered on the surface of the catalyst, which not only results in the formation of the less Cu active species but inhibits the interaction between Cu species and CeO₂. In addition, the optimal CuCe-SF-N catalyst displays relative stability during the 200 h time-on-stream test even in the presence of H₂O and CO₂.     

Ceria supported ruthenium nanoparticles: Remarkable catalyst for H2 evolution from dimethylamine borane

Ceria supported ruthenium nanoparticles (Ru⁰/CeO₂) are synthesized by impregnation of Ru³⁺ ions on CeO₂ powders followed by sodium borohydride reduction of Ru³⁺/CeO₂. Their characterization was achieved using analytical methods including TEM, XRD, BET, SEM, and XPS. All the results reveal the formation of ruthenium(0) nanoparticles in 1.8 ± 0.3 nm size on CeO₂ support. Ru⁰/CeO₂ nanoparticles show high activity in catalyzing the H₂ evolution from dimethylamine borane (DMAB). Ru⁰/CeO₂ nanoparticles with 0.55% wt Ru provide the highest turnover frequency (812 h⁻¹) for releasing H₂ from DMAB at 60 °C and a total of 2500 turnovers before deactivation. High activity of Ru⁰/CeO₂ nanoparticles for catalytic dehydrogenation of DMAB is attributable to the reducible nature of CeO₂ support. Ce³⁺ defects formation in ceria under reducing conditions of dehydrogenation causes accumulation of negative charge on the oxide support, which makes oxide surface attractive for the ruthenium(0) nanoparticles. This, in turn, causes an enhancement in the metal-support interaction and thus in catalytic activity. The XPS analysis of bare ceria and Ru⁰/CeO₂ demonstrates the increase in the concentration of Ce³⁺ defects after catalysis. Ru⁰/CeO₂ nanoparticles are also reusable catalyst for H₂ evolution from DMAB retaining 40% of initial activity after 4th run of reaction. The catalytic activity of Ru⁰/CeO₂ nanoparticles and activation energy of catalytic dehydrogenation are compared with those of the other ruthenium based catalysts known in literature.