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.     

Oxidative steam reforming of ethanol over Ni/Al2O3 catalysts promoted by CeO2, ZrO2 and CeO2–ZrO2

Oxidative steam reforming of ethanol at low oxygen to ethanol ratios was investigated over nickel catalysts on Al₂O₃ supports that were either unpromoted or promoted with CeO₂, ZrO₂ and CeO₂–ZrO₂. The promoted catalysts showed greater activity and a higher hydrogen yield than the unpromoted catalyst. The characterization of the Ni-based catalysts promoted with CeO₂ and/or ZrO₂ showed that the variations induced in the Al₂O₃ by the addition of CeO₂ and/or ZrO₂ alter the catalyst's properties by enhancing Ni dispersion and reducing Ni particle size. The promoters, especially CeO₂–ZrO₂, improved catalytic activity by increasing the H₂ yield and the CO₂/CO and the H₂/CO values while decreasing coke formation. This results from the addition of ZrO₂ into CeO₂. This promoter highlights the advantages of oxygen storage capacity and of mobile oxygen vacancies that increase the number of surface oxygen species. The addition of oxygen facilitates the reaction by regenerating the surface oxygenation of the promoters and by oxidizing surface carbon species and carbon-containing products.     

Carbon deposition on Ni/ZrO2–CeO2 catalyst during steam reforming of acetic acid

Steam reforming of acetic acid, one model compounds of bio-oil, was studied on the Ni/ZrO₂–CeO₂ catalysts which were prepared by the impregnation method. The results showed that high acetic acid conversion and hydrogen yield were obtained in the temperature range of 650–750 °C when H₂O/HAC ratio was 3. Nevertheless, the catalyst deactivation was caused by carbon deposition eventually with time-on-stream. In order to discuss the behavior of the carbon deposition on the Ni/ZrO₂–CeO₂ catalyst during steam reforming of bio-oil, the structure and morphology of carbon deposition were investigated by BET, XRD, TG/DTA, TPR, SEM and EDX techniques. All the experimental results showed acetone and CO were the important carbon precursors of acetic acid reforming and the graphitic-like carbon was the main type of carbon deposition on the surface of the deactivated 12%Ni/CeO₂–ZrO₂ catalyst.     

Novel Ni–ZrO2 catalyst doped with Yb2O3 for ethanol steam reforming

A type of Yb₂O₃ doped Ni–ZrO₂ catalyst for ethanol steam reforming was developed, and displayed excellent catalyzing performance for the selective formation of H₂ and CO₂. Over a Ni_1.25Zr₁Yb_0.8 catalyst, STY(H₂) can maintain stable at the level of 0.396 mol h⁻¹ g⁻¹ (data taken 120 h after the reaction started) under the reaction conditions of 0.5 MPa and 723 K, which was 1.6 times that (0.247 mol h⁻¹ g⁻¹) of the Yb-free counterpart Ni_1.25Zr₁. Characterization of the catalyst revealed that dissolution of an appropriate amount of Yb³⁺ ions in the zirconia host resulted in the formation of the Zr–Yb composite oxide with cubic-ZrO₂ structure, c-(Zr–Yb)O_z, which inhibited effectively the transformation of c-ZrO₂ to thermodynamically more stable m-ZrO₂, thus avoiding sintering of the (Zr–Yb)O_z composite. It was demonstrated that the doping of Yb₂O₃ to Ni–ZrO₂ changed also the valence states or the micro-environments of the Ni-species at the quasi-active surface of the tested catalyst, which was conducive to inhibiting agglomeration of the Ni_x⁰–Niⁿ⁺ species active catalytically, with resulting in maintaining the high metallic nickel dispersion and inhibiting coking. The aforementioned two factors both contributed to improving the activity and operating stability as well as heat-resistant quality of the catalyst.     

Hydrogen production by steam reforming of ethanol over mesoporous Ni–Al2O3–ZrO2 aerogel catalyst

A mesoporous Ni–Al₂O₃–ZrO₂ aerogel (Ni–AZ) catalyst was prepared by a single-step epoxide-driven sol–gel method and a subsequent supercritical CO₂ drying method. For comparison, a mesoporous Al₂O₃–ZrO₂ aerogel (AZ) support was prepared by a single-step epoxide-driven sol–gel method, and subsequently, a mesoporous Ni/Al₂O₃–ZrO₂ aerogel (Ni/AZ) catalyst was prepared by an incipient wetness impregnation method. The effect of preparation method on the physicochemical properties and catalytic activities of Ni–AZ and Ni/AZ catalysts was investigated. Although both catalysts retained a mesoporous structure, Ni/AZ catalyst showed lower surface area than Ni–AZ catalyst. From TPR, XRD, and H₂–TPD results, it was revealed that Ni–AZ catalyst retained higher reducibility and higher nickel dispersion than Ni/AZ catalyst. In the hydrogen production by steam reforming of ethanol, both catalysts showed a stable catalytic performance with complete conversion of ethanol. However, Ni–AZ catalyst showed higher hydrogen yield than Ni/AZ catalyst. Superior textural properties, high reducibility, and high nickel surface area of Ni–AZ catalyst were responsible for its enhanced catalytic performance in the steam reforming of ethanol.     

Rh promoted and ZrO2/Al2O3 supported Ni/Co based catalysts: High activity for CO2 reforming,steam–CO2 reforming and oxy–CO2 reforming of CH4

Ni (2.5 wt%) and Co (2.5 wt%) supported over ZrO₂/Al₂O₃ were prepared by following a hydrolytic co-precipitation method. The synthesized catalysts were further promoted by Rh incorporation (0.01–1.00 wt%) and tested for their catalytic performance for dry CO₂ reforming, combined steam–CO₂ reforming and oxy–CO₂ reforming of methane for production of syngas. The catalysts were characterized by using N₂ physical adsorption, XRD, H₂–TPR, SEM, CO₂–TPD, NH₃–TPD, TEM and TGA. The results revealed that ZrO₂ phase was in crystalline form in the catalysts along with amorphous Al oxides. Ni and Co were confirmed to be in their respective spinel phases that were reducible to metallic form at 800 °C under H₂. Ni and Co were well dispersed with their nano-crystalline nature. The catalyst with 0.2% loading of Rh showed superior performance in the studied reactions for reforming of methane. This catalyst also showed good coke resistance ability for dry CO₂ reforming reaction with 3.8 wt% of carbon formation during the reaction as compared to 11.6 wt% carbon formation over the catalyst without Rh. The catalyst performance was stable throughout the reaction time for CH₄ conversions, irrespective of carbon formation with slight decline (～1%) in CO₂ conversion. For dry CO₂ reforming reaction, this catalyst showed good conversion for both CH₄ and CO₂ (67.6% and 71.8% respectively) with a H₂/CO ratio of 0.84, while for the Oxy-CO₂ reforming reaction, the activity was superior with CH₄ and CO₂ conversions (73.7% and 83.8% respectively) and H₂/CO ratio of 1.05.     

Hydrogen production by steam reforming of dimethyl ether over ZnO–Al2O3 bi-functional catalyst

A series of ZnO–Al₂O₃ catalysts with various ZnO/(ZnO + Al₂O₃) molar ratios have been developed for hydrogen production by dimethyl ether (DME) steam reforming within microchannel reactor. The catalysts were characterized by N₂ adsorption-desorption, X-ray diffraction and temperature programmed desorption of NH₃. It was found that the catalytic activity was strongly dependent on the catalyst composition. The overall DME reforming rate was maximized over the catalyst with ZnO/(ZnO + Al₂O₃) molar ratio of 0.4, and the highest H₂ space time yield was 315 mol h⁻¹·kg_cat⁻¹ at 460 °C. A bi-functional mechanism involving catalytic active site coupling has been proposed to account for the phenomena observed. An optimized bi-functional DME reforming catalyst should accommodate the acid sites and methanol steam reforming sites with a proper balance to promote DME steam reforming, whereas all undesired reactions should be impeded without sacrificing activity. This work suggests that an appropriate catalyst composition is mandatory for preparing good-performance and inexpensive ZnO–Al₂O₃ catalysts for the sustainable conversion of DME into H₂-rich reformate.     

H2 and CO production over a stable Ni–MgO–Ce0.8Zr0.2O2 catalyst from CO2 reforming of CH4

Ni–Ce_0.8Zr_0.2O₂ and Ni–MgO–Ce_0.8Zr_0.2O₂ catalysts were investigated for H₂ production from CO₂ reforming of CH₄ reaction at a very high gas hourly space velocity of 480,000 h⁻¹. Ni–MgO–Ce_0.8Zr_0.2O₂ exhibited higher catalytic activity and stability (CH₄ conversion >95% at 800 °C for 200 h). The outstanding catalytic performance is mainly due to the basic nature of MgO and an intimate interaction between Ni and MgO.     

The effect of preparation method on the catalytic performance over superior MgO-promoted Ni–Ce0.8Zr0.2O2 catalyst for CO2 reforming of CH4

The effect of preparation method on MgO-promoted Ni–Ce_0.8Zr_0.2O₂ catalysts was investigated in CO₂ reforming of CH₄. Co-precipitated Ni–MgO–Ce_0.8Zr_0.2O₂ exhibited very high activity as well as stability (X_CH4 > 95% at 800 °C for 200 h) due to high surface area, high dispersion of Ni, small Ni crystallite size, and easier reducibility. Four elements (Ni, Mg, Ce, and Zr) are located at the same position for the co-precipitated catalyst, resulting in easier reducibility.     

Plasma-reduced Ni/γ–Al2O3 and CeO2–Ni/γ–Al2O3 catalysts for improving dry reforming of propane

Pristine Ni/γ–Al₂O₃ and CeO₂–Ni/γ–Al₂O₃ catalysts were prepared by co-impregnation technique for dry reforming of propane. X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) were used to examine the structure and morphology of the catalysts before and after the reforming reactions. The excellent interaction between catalyst active phases was observed in both CeO₂–Ni/γ–Al₂O₃ and Ni/γ–Al₂O₃ stabilized with polyethelene glycol (Ni/γ–Al₂O₃–PEG). Towards C₃H₈ and CO₂ conversion, the CeO₂–Ni/γ–Al₂O₃ and Ni/γ–Al₂O₃–PEG showed improved catalytic activity when compared to the pristine Ni/γ–Al₂O₃ catalyst. Interestingly, high H₂ concentration was achieved with the CeO₂–Ni/γ–Al₂O₃ and high CO concentration with the Ni/γ–Al₂O₃–PEG, which is due to the nanoconfinement of nickel particles within the support and favorable metal-support interaction as a result of plasma reduction. The CeO₂–Ni/γ–Al₂O₃ catalyst exhibited better stability for anti-sintering and coke resistance, thus exhibiting high reactivity and durability in the dry reforming.     

Synthesis and characterization of bimetallic Cu–Ni/ZrO2 nanocatalysts: H2 production by oxidative steam reforming of methanol

Cu/ZrO₂, Ni/ZrO₂ and bimetallic Cu–Ni/ZrO₂ catalysts were prepared by deposition–precipitation method to produce hydrogen by oxidative steam reforming of methanol (OSRM) reaction in the range of 250–360 °C. TPR analysis of the Cu–Ni/ZrO₂ catalyst showed that the presence of Cu facilitates the reduction of the Ni at lower temperatures. In addition, this sample showed two reduction peaks, the former peak was attributed to the reduction of the adjacent Cu and Ni atoms which could be forming a bimetallic Cu-rich phase, and the second was assigned to the remaining Ni atoms forming bimetallic Ni-rich nanoparticles. Transmission Electron Microscopy revealed Cu or Ni nanoparticles on the monometallic samples, while bimetallic nanoparticles were identified on the Cu–Ni/ZrO₂ catalyst. On the other hand, Cu–Ni/ZrO₂ catalyst exhibited better catalytic activity than the monometallic samples. The difference between them was related to the Cu–Ni nanoparticles present on the former catalyst, as well as the bifunctional role of the bimetallic phase and the support that improve the catalytic activity. All the catalysts showed the same selectivity toward H₂ at the maximum reaction temperature and it was ∼60%. The high selectivity toward CO is associated to the presence of the bimetallic Ni-rich nanoparticles, as evidenced by TEM–EDX analysis, since this behavior is similar to the one showed by the monometallic Ni-catalyst.     

The surfactant-assisted Ni–Al2O3 catalyst prepared by a homogeneous precipitation method for CH4 steam reforming

The surfactant-assisted Ni–Al₂O₃ catalysts are prepared by the homogeneous precipitation method with a surfactant/Al molar ratio ranging from 0.0 to 2.0. It has been investigated the effects of the surfactant on the physicochemical properties and the catalytic activities of the Ni–Al₂O₃ catalysts. The BET surface area of the catalysts decreases with increasing the surfactant content. The pore volume and pore size of the catalysts increase with increasing the surfactant content. XRD results indicate that all of the catalysts exhibit strong diffraction peaks corresponding to NiO and weak peaks corresponding to NiAl₂O₄. In the TPR results, the reduction peaks which indicates that the Ni particles strongly interacted with the support are present at between 668 and 688 °C. The activities of the prepared catalysts for methane steam reforming increase with increasing surfactant content in fresh and poisoned state due to an increase of pore volume and pore size.     

Chemical-looping steam methane reforming over macroporous CeO2–ZrO2 solid solution: Effect of calcination temperature

Chemical-looping steam methane reforming (CL-SMR) is a novel process for the co-production of pure hydrogen and syngas without purification processes. A series of CeO₂–ZrO₂ mixed oxides were prepared by colloidal crystal templating method with calcination temperature increasing from 450 to 850 °C. The structural characteristic and reducibility of CeO₂–ZrO₂ oxygen carriers were investigated by SEM, XRD and TPR techniques and correlated to their reactivity for CL-SMR. The CeO₂–ZrO₂ mixed oxides calcined at low temperatures (e.g., 450 °C) exhibit a better uniform and three-dimensionally ordered macroporous structure, which enhance the mobility of oxygen species, improving the reducibility of CeO₂–ZrO₂ oxygen carriers. The ordered macroporous structure can lead to a high reactivity for CL-SMR, especially for the hydrogen production in water splitting reaction. It was found that the Ce–Zr-450 sample showed the best performance for H₂ production. After ten redox CL-SMR cycles at 800 °C, the Ce–Zr-450 sample still maintained relatively high hydrogen yield and the three-dimensionally ordered macroporous structure remained in good condition, indicating high reactivity and structural stability.     

Efficient catalytic abatement of greenhouse gases: Methane reforming with CO2 using a novel and thermally stable Rh–CeO2 catalyst

2% Rh–CeO₂ catalyst was synthesized using the hard template method and characterized by means of N₂ adsorption/desorption, XRD and H₂-TPR methods. The prepared powdered catalyst exhibited high thermal stability and high surface area with negligible sintering during 24-h exposure to 973 K in an inert atmosphere. During the temperature programmed methane dry reforming reaction between 473 and 1073 K, an increase in the molar H₂/CO ratio from 0.3 at 623 K to as high as 0.96 at 1073 K was observed. Besides H₂ and CO, H₂O was identified among reaction products, originating from the simultaneously occurring reverse water-gas shift reaction. During the isothermal test performed at 923 K, the 2% Rh–CeO₂ catalyst exhibited stable performance and produced syngas with the average H₂/CO ratio equal to 0.62. A relative drop of catalyst activity equal to 11% was observed within 70-h time on stream at 1023 K, with the average H₂/CO ratio at the reactor outlet equal to 0.71.     

Effects of noble metal-doping on Ni/La2O3–ZrO2 catalysts for dry reforming of coke oven gas

A series of noble metal (Ru, Pd, Ag) doped Ni catalysts supported on La₂O₃–ZrO₂ mixed oxide were prepared using the sol–gel method and evaluated for use in dry reforming of coke oven gas (COG). The catalysts were investigated by means of N₂ adsorption–desorption, XRD, H₂-TPR, TPH, TEM and TG–DSC. TPH analysis revealed that two carbonaceous species formed on the used catalysts and that the low-temperature carbon species was sufficiently active for the reforming reaction. TEM observations indicated that highly dispersed and small metal particles were formed, suppressing coke deposition and improving catalytic performance. The test results indicated that the addition of trace amounts of noble metals effectively promotes catalytic activity. The 0.1Ru–10Ni/8LZ catalyst showed the highest performance among the bimetallic catalysts, because of the strong synergetic effect between Ru and Ni via the formation of a Ru–Ni alloy, which will be promising catalysts in the catalytic dry reforming of COG.     

CuO–CeO2 catalysts synthesized in one-step: Characterization and PROX performance

PEM fuel cells seem to be the most affordable and commercially viable hydrogen-based cells, the biggest challenge being to obtain CO-free H₂ (<100 ppm) as the fuel. In this study, the use of CuO–CeO₂ catalysts in preferential oxidation of CO to obtain CO-free H₂ (PROX reaction) was investigated. Ce_1−xCu_xO₂ catalysts, with x (mol%) = 0, 0.01, 0.03, 0.05 and 0.10, were synthesized in one-step by the polymeric precursor method, to obtain a very fine dispersion and strong metal-support interaction, to favor active copper species and a preference for the PROX reaction. The results obtained from catalyzed reactions and characterization of the catalysts by XRD, Rietveld refinement, BET surface area, UV–Vis and TPR, suggest that this one-step synthesis method gives rise to catalysts with copper species selective for the PROX reaction, which reaches a maximum rate on Ce_0.97Cu_0.03O₂ catalyst.     

Hydrogen production from catalytic steam reforming of bio-oil aqueous fraction over Ni/CeO2–ZrO2 catalysts

A series of composite catalysts Ni/CeO₂–ZrO₂ were prepared via impregnation method with Ni as the active metal. A laboratory-scale fixed-bed reactor was employed to investigate the catalyst performance during hydrogen production by steam reforming bio-oil aqueous fraction. Effects of water-to-bio-oil ratio (W/B), reaction temperature, and the loaded weight of Ni and Ce on the hydrogen production performance of Ni/CeO₂–ZrO₂ catalysts were examined. The obtained results were compared with commercial nickel-based catalysts (Z417). The best performance of Ni/CeO₂–ZrO₂ catalyst was observed when the Ni and Ce loaded weight were 12% and 7.5% respectively. At W/B = 4.9, T = 800 °C, H₂ yield reaches the highest of 69.7% and H₂ content of 61.8% were obtained. Under the same condition, H₂ yield and H₂ content were higher than commercial nickel-based catalysts (Z417).     

Characterization and activity test of commercial Ni/Al2O3, Cu/ZnO/Al2O3 and prepared Ni–Cu/Al2O3 catalysts for hydrogen production from methane and methanol fuels

In this study, methane and methanol steam reforming reactions over commercial Ni/Al₂O₃, commercial Cu/ZnO/Al₂O₃ and prepared Ni–Cu/Al₂O₃ catalysts were investigated. Methane and methanol steam reforming reactions catalysts were characterized using various techniques. The results of characterization showed that Cu particles increase the active particle size of Ni (19.3 nm) in Ni–Cu/Al₂O₃ catalyst with respect to the commercial Ni/Al₂O₃ (17.9). On the other hand, Ni improves Cu dispersion in the same catalyst (1.74%) in comparison with commercial Cu/ZnO/Al₂O₃ (0.21%). A comprehensive comparison between these two fuels is established in terms of reaction conditions, fuel conversion, H₂ selectivity, CO₂ and CO selectivity. The prepared catalyst showed low selectivity for CO in both fuels and it was more selective to H₂, with H₂ selectivities of 99% in methane and 89% in methanol reforming reactions. A significant objective is to develop catalysts which can operate at lower temperatures and resist deactivation. Methanol steam reforming is carried out at a much lower temperature than methane steam reforming in prepared and commercial catalyst (275–325 °C). However, methane steam reforming can be carried out at a relatively low temperature on Ni–Cu catalyst (600–650 °C) and at higher temperature in commercial methane reforming catalyst (700–800 °C). Commercial Ni/Al₂O₃ catalyst resulted in high coke formation (28.3% loss in mass) compared to prepared Ni–Cu/Al₂O₃ (8.9%) and commercial Cu/ZnO/Al₂O₃ catalysts (3.5%).     

CO2 reforming of CH4 by combination of cold plasma jet and Ni/γ-Al2O3 catalyst

CO₂ reforming of CH₄ to synthesis gas was investigated by cold plasma jet (CPJ) only and combination of cold plasma jet with Ni/γ-Al₂O₃ catalyst at atmospheric pressure. The higher selectivity of H₂ and CO, and higher energy efficiency was obtained by this novel process. The optimum experimental conditions are: CH₄ = 3.33 Nl/min, CO₂ = 5.00 Nl/min, N₂ = 8.33 Nl/min, and the input power at 770 W. The results showed that, for the plasma only, the conversions of CH₄ and CO₂ were 46% and 34%, the selectivities of CO and H₂ were 85% and 78%, the energy efficiency was 2.9 mmol/kJ, respectively; for the combination of cold plasma jet with Ni/γ-Al₂O₃ catalyst, the conversions of CH₄ and CO₂ were increased by 14% and 6%, the yield of H₂ and CO increased by 18% and 11%, the energy efficiency reached at 3.7 mmol/kJ, respectively. And the catalyst hasn't accessorial heating. The CPJ method has the advantage of simple processing and is easy to be industrialized.     

Production of syngas via autothermal reforming of methane in a fluidized-bed reactor over the combined CeO2–ZrO2/SiO2 supported Ni catalysts

Production of syngas via autothermal reforming of methane (MATR) in a fluidized bed reactor was investigated over a series of combined CeO₂–ZrO₂/SiO₂ supported Ni catalysts. These combined CeO₂–ZrO₂/SiO₂ supports and supported Ni catalysts were characterized by nitrogen adsorption, XRD, NH₃-TPD, CO₂-TPD and H₂-TPR. It was found that the combined supports integrated the advantages of SiO₂ and CeO₂, ZrO₂. That is, they have bigger surface area (about 300 m²/g) than pure CeO₂ and ZrO₂, stronger acidity and alkalescence than that of pure SiO₂, and enhanced the mobility of H adatoms. Ni species dispersed highly on these combined CeO₂–ZrO₂/SiO₂ supports, and became more reducible. Ni catalysts on the combined supports possess higher CO₂ adsorption ability, higher methane activation ability and exhibited higher activity for MATR. H₂/CO ratio in product gas could be controlled successfully in the range of 0.99–2.21 by manipulating the relative concentrations of CO₂ and O₂ in feed.