Monolithic Pt/Ce0.8Zr0.2O2/cordierite catalysts for low temperature water gas shift reaction in the real reformate

Monolithic catalysts were prepared by washcoating Ce_0.8Zr_0.2O₂ slurries and then impregnating platinum or rhenium onto cordierite substrates, and characterized by Brunauer–Emmett–Teller (BET), X-ray diffraction (XRD), inductively coupled plasma (ICP), temperature-programmed-reduction (TPR) and temperature-programmed deposition of CO (CO-TPD) techniques. The effects of preparation parameters on the catalytic performance for water gas shift (WGS) reaction were investigated in details, including different Ce_0.8Zr_0.2O₂ powder as washcoat, coat loadings, metal loadings, Pt/Re weight ratio and impregnation sequences. In addition, pyrophoricity (exposure to oxygen stream) and long-term stability were carried out over monolithic catalysts with the optimized composition. The results showed that Ce_0.8Zr_0.2O₂ prepared by microemulsion methods was the preferred washcoat, and that 50 wt% Ce_0.8Zr_0.2O₂ coat loading and 0.68 wt% Pt loading were required to reduce CO content to ca. 1%. The optimal catalytic performance was achieved over 0.11 wt% Re/0.34 wt% Pt/50 wt% Ce_0.8Zr_0.2O₂–M/cordierite catalyst. Pyrophoricity tests indicated that no obvious activity loss was observed over 0.11 wt% Re/0.34 wt% Pt/50 wt% Ce_0.8Zr_0.2O₂–M/cordierite catalyst after three exposures to oxygen; while 17% of the initial activity was lost over industrial B206 after one exposure. Monolithic 0.11 wt% Re/0.34 wt% Pt/50 wt% Ce_0.8Zr_0.2O₂–M/cordierite catalyst exhibited good stability during 80 h on-stream test.     

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.     

Effects of Ce/Zr composition on nickel based Ce(1−x)ZrxO2 catalysts for hydrogen production in sulfur–iodine cycle

In this study, 5%Ni/Ce_(1−x)Zr_xO₂( x = 0, 0.2, 0.5, 0.8, 1) catalysts were prepared by sol–gel method and tested for hydrogen iodide (HI) decomposition in sulfur–iodine (SI) cycle. The effects of zirconia incorporation were subsequently examined by a series of characterization methods. In comparison with the blank test, all of the catalysts, particularly Ni/Ce_0.8Zr_0.2O₂, remarkably enhance the HI decomposition. Therefore, adding a small amount of zirconia results in the highest catalytic activity, which could be attributed to the following three effects: increase in oxygen mobility and oxygen vacancy, stronger interaction between NiO and the supports. The oxygen mobility and oxygen vacancy are dominant in the HI decomposition. The strong interaction between NiO and the supports accelerates the oxygen transfer from the bulk to surface, which could also enhance the decomposition. However, excessive zirconia content has negative effects, which is due to the decrease in oxygen mobility and surface area. The poor thermal stability in zirconia-rich supports also restricts catalytic performance. In addition, a hypothetic mechanism of HI catalytic decomposition over Ni/Ce_(1−x)Zr_xO₂ is proposed.     

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.     

Comparative study of CuO supported on CeO2, Ce0.8Zr0.2O2 and Ce0.8Al0.2O2 based catalysts in the CO-PROX reaction

CuO supported on CeO_2, Ce_0.8Zr_0.2O₂ and Ce_0.8Al_0.2O₂ based catalysts (6%wt Cu) were synthesized and tested in the preferential oxidation of CO in a H₂-rich stream (CO-PROX). Nanocrystalline supports, CeO₂ and solid solutions of modified CeO₂ with zirconium and aluminum were prepared by a freeze-drying method. CuO was supported by incipient wetness impregnation and calcination at 400 °C. All catalysts exhibit high activity in the CO-PROX reaction and selectivity to CO₂ at low reaction temperature, being the catalyst supported on CeO₂ the more active and stable. The influence of the presence of CO₂ and H₂O was also studied.     

Synthesis gas production from dry reforming of methane over Ce0.75Zr0.25O2-supported Ru catalysts

Ce_0.75Zr_0.25O₂ solid solution supported Ru catalysts were prepared and tested for CH₄–CO₂ reforming. The effect of Ru content on the properties of the catalysts was investigated by means of N₂ adsorption–desorption, H₂-TPR/MS, XRD, XPS, CO chemisorption and H₂-TPD/MS. It was found that the highly dispersed Ru species favored the interaction between Ru and Ce_0.75Zr_0.25O₂. The reduced Ce_0.75Zr_0.25O₂ was able to store hydrogen, while Ru promoted the reduction of Ce_0.75Zr_0.25O₂. Under the identical conditions, the CH₄ and CO₂ conversions of the catalysts increased with the increase of Ru content, however, the turnover frequencies of CH₄ and CO₂ were higher for the catalysts with lower Ru contents, which may be resulted from the strong interaction between Ru and Ce_0.75Zr_0.25O₂. The Ru catalyst exhibited good stability and excellent resistance to carbon deposition. Remarkably, zirconium and cerium hydrides were detected in the used catalyst, which may participate in the elimination of the carbon deposit. Apart from the nature of metallic Ru and the redox property of Ce_0.75Zr_0.25O₂, we suggest that the excellent resistance of the catalyst to carbon deposition is also attributed to the hydrogen storage of the reduced Ce_0.75Zr_0.25O₂.     

Enhanced low temperature catalytic activity of Ni/Al–Ce0.8Zr0.2O2 for hydrogen production from ammonia decomposition

Ammonia decomposition is an effective way for high purity hydrogen production, yet the increase of catalytic activity at low temperatures remains a big challenge for this process. In this paper, a CeO₂–ZrO₂ composite with Al as the secondary dopant was synthesized by the co-precipitation method, which was used as the carrier of nickel metal for ammonia decomposition. The experimental results showed that an obvious increase in catalytic activity of the ammonia decomposition at the relatively low temperature range of 450–550 °C was achieved over the nickel catalyst with CeO₂–ZrO₂ composite as the metal carrier. Specifically, the complete decomposition of ammonia was achieved at 580 °C for Ni/Al–Ce_0.8Zr_0.2O₂ catalyst, while only 92% of ammonia was decomposed at 600 °C over the reference Ni/Al₂O₃ catalyst. The characterization results indicated that the introduction of Al as the secondary dopant of ceria not only increases the specific surface area and oxygen defects on the surface, but also enhances the nickel metal dispersion and metal-support interaction, thus enhances the catalytic performance of Ni/Al–Ce_0.8Zr_0.2O₂ catalyst in the ammonia decomposition.     

Proton-conducting fuel cells operating on hydrogen,ammonia and hydrazine at intermediate temperatures

Anode-supported proton-conducting fuel cell with BaZr_0.1Ce_0.7Y_0.2O_3−δ (BZCY) electrolyte and Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ (BSCF) cathode was fabricated. Peak power densities of ∼420 and 135 mW/cm² were achieved, respectively, at 700 and 450 °C for a cell with 35 μm thick electrolyte operating on hydrogen fuel. The endothermic nature of the ammonia decomposition reaction, however, resulted in cell temperature 30–65 °C lower than the furnace when operating on ammonia. Accounting the cooling effect, comparable power density was achieved for the cell operating on ammonia and hydrogen at high temperature. At reduced temperature, the cell demonstrated worse performance when operating on ammonia than on hydrogen due to the poor activity of the anode towards NH₃ catalytic decomposition. By applying on-line catalytic decomposition products of N₂H₄ as the fuel, similar cell performance to that with NH₃ fuel was also observed.     

Methane dry reforming on Ni/Ce0.75Zr0.25O2–MgAl2O4 and Ni/Ce0.75Zr0.25O2–γ-alumina: Effects of support composition and water addition

Nickel catalysts (10wt.%) supported on MgAl₂O₄ and γ-Al₂O₃ were prepared by the wet impregnation method and promoted with various contents of Ce_0.75Zr_0.25O₂. X-ray diffraction (XRD), BET surface area, scanning electron microscopy (SEM), thermal gravimetric analysis (TGA), H₂-temperature programmed reduction (TPR) and CO₂-temperature programmed desorption (TPD) were employed to observe the characteristics of the prepared catalysts. Ni/γ-Al₂O₃ and Ni/Ce_0.75Zr_0.25O₂ (5wt.%)–MgAl₂O₄ showed better activity in CO₂ methane reforming with 75.7(0.93) and 75.4(0.82) CH₄ conversions (and H₂/CO ratio). H₂O was added to feed in the range of H₂O/(CH₄ + CO₂): 0.1–0.5 to suppress reverse water gas shift (RWGS) effect and adjusting H₂/CO ratio. The CH₄ conversions (and H₂/CO) increased to 81(1.1) with 0.5 water/carbon mole ratio in Ni/γ-Al₂O₃ and 85(1.2) with 0.2 water/carbon mole ratio in Ni/Ce_0.75Zr_0.25O₂ (5wt.%)–MgAl₂O₄. The stability of Ni/Ce_0.75Zr_0.25O₂ (5wt.%)–MgAl₂O₄ in the presence and absence of water was investigated. Coke formation and amount in used catalysts were examined by SEM and TGA, respectively. The results showed that the amount of carbon was suppressed and negligible coke formation (less than 3%) was observed in the presence of 0.2 water/carbon mole ratio over Ni/Ce_0.75Zr_0.25O₂ (5wt.%)–MgAl₂O₄ catalyst.     

Development of a Ni-Ce0.8Zr0.2O2 catalyst for solid oxide fuel cells operating on ethanol through internal reforming

Inexpensive 20 wt.% Ni-Ce_0.8Zr_0.2O₂ catalysts are synthesized by a glycine nitrate process (GNP) and an impregnation process (IMP). The catalytic activity for ethanol steam reforming (ESR) at 400-650 °C, catalytic stability and carbon deposition properties are investigated. Ni-Ce_0.8Zr_0.2O₂ (GNP) shows a higher catalytic performance than Ni-Ce_0.8Zr_0.2O₂ (IMP), especially at lower temperatures. It also presents a better coking resistance and a lower graphitization degree of the deposited carbon. The superior catalytic activity and coke resistance of Ni-Ce_0.8Zr_0.2O₂ (GNP) is attributed to the small particle size of the active metallic nickel phase and the strong interaction between the nickel and the Ce_0.8Zr_0.2O₂ support, as evidenced by the XRD and H₂-TPR. The Ni-Ce_0.8Zr_0.2O₂ (GNP) is further applied as an anode functional layer in solid oxide fuel cells operating on ethanol steam. The cell yields a peak power density of 536 mW cm⁻² at 700 °C when operating on EtOH-H₂O gas mixtures, which is only slightly lower than that of hydrogen fuel, whereas the cell without the functional layer failed for short-term operations. Ni-Ce_0.8Zr_0.2O₂ (GNP) is promising as an active and highly coking-resistant catalyst layer for solid-oxide fuel cells operating on ethanol steam fuel.     

Water–gas shift reaction over Pt and Pt–CeOx supported on CexZr1−xO2

The water–gas shift (WGS) reaction was examined over Pt and Pt–CeO_x catalysts supported on Ce_xZr_1−xO₂ (Ce_0.05Zr_0.95O₂, Ce_0.2Zr_0.8O₂, Ce_0.4Zr_0.6O₂, Ce_0.6Zr_0.4O₂, Ce_0.7Zr_0.3O₂ and Ce_0.8Zr_0.2O₂) under severe reaction conditions, viz. 6.7 mol% CO, 6.7 mol% CO₂, and 33.2 mol% H₂O in H₂. The catalysts were characterized with several techniques, including X-ray diffraction (XRD), CO chemisorption, temperature-programmed reduction (TPR) with H₂, temperature-programmed oxidation (TPO), inductively coupled plasma-atomic emission spectroscopy (ICP-AES) and bright-field transmission electron microscopy (TEM). Among the supported Pt catalysts tested, Pt/Ce_0.4Zr_0.6O₂ showed the highest WGS activity in all temperature ranges. An improvement in the WGS activity was observed when CeO_x was added with Pt on Ce_xZr_1−xO₂ supports (x = 0.05 and 0.2) due to intimate contact between Pt and CeO_x species. Based on CO chemisorptions and TPR profiles, it has been found that the interaction between Pt species and surface ceria-zirconia species is beneficial to the WGS reaction. A gradual decrease in the catalytic activity with time-on-stream was found over Pt and Pt–CeO_x catalysts supported on Ce_xZr_1−xO₂, which can be explained by a decrease in the Pt dispersion. The participation of surface carbonate species on deactivation appeared to be minor because no improvement in the catalytic activity was found after the regeneration step where the aged catalyst was calcined in 10 mol% O₂ in He at 773 K and subsequently reduced in H₂ at 673 K.     

Reforming of bioethanol over Ni/Al2O3 and Ni/CeZrO2/Al2O3 catalysts in supercritical water for hydrogen production

Bioethanol was reformed in supercritical water (SCW) at 500 °C and 25 MPa on Ni/Al₂O₃ and Ni/CeZrO₂/Al₂O₃ catalysts to produce high-pressure hydrogen. The results were compared with non-catalytic reactions. Under supercritical water and in a non-catalytic environment, ethanol was reformed to H₂, CO₂ and CH₄ with small amounts of CO and C2 gas and liquid products. The presence of either Ni/Al₂O₃ or Ni/CeZrO₂/Al₂O₃ promoted reactions of ethanol reforming, dehydrogenation and decomposition. Acetaldehyde produced from the decomposition of ethanol was completely decomposed into CH₄ and CO, which underwent a further water-gas shift reaction in SCW. This led to great increases in ethanol conversion and H₂ yield on the catalysts of more than 3-4 times than that of the non-catalytic condition. For the catalytic operation, adding small amounts of oxygen at oxygen to ethanol molar ratio of 0.06 into the feed improved ethanol conversion, at the expense of some H₂ oxidized to water, resulting in a slightly lower H₂ yield. The ceria-zirconia promoted catalyst was more active than the unpromoted catalyst. On the promoted catalyst, complete ethanol conversion was achieved and no coke formation was found. The ceria-zirconia promoter has important roles in improving the decomposition of acetaldehyde, the enhancement of the water-gas shift as well as the methanation reactions to give an extremely low CO yield and a tremendously high H₂/CO ratio. The SCW environment for ethanol reforming caused the transformation of gamma-alumina towards the corundum phase of the alumina support in the Ni/Al₂O₃ catalyst, but this transformation was slowed down by the presence of the ceria-zirconia promoter.     

Highly efficient Zr-substituted catalysts CuZnAl1−xZrxO used for hydrogen production via dimethyl ether steam reforming

A series of CuZnAl_1−xZr_xO catalysts with different weight ratios of ZrO₂/(Al₂O₃ + ZrO₂) were prepared by co-precipitation and used for catalytic production of hydrogen via the route of dimethyl ether steam reforming (DME SR). Multiple techniques such as N₂ physisorption, X-ray diffraction (XRD), temperature-programmed reduction by hydrogen (H₂-TPR), N₂O chemisorption and X-ray absorption fine structure (XAFS, including XANES and EXAFS) were employed for catalyst characterization. It is found that the relative contents of Al and Zr greatly influence the catalytic performance of the catalysts including DME conversion, H₂ yield and CO/CO₂ selectivity. The catalyst CuZnAl_0.8Zr_0.2O shows not only the highest DME conversion but also the highest H₂ yield in the whole reaction temperature region of 300–425 °C. Poorly crystallized CuO and ZnO phases were identified by XRD for CuZnAl_1−xZr_xO catalysts. The crystallinity of them increases with the decrease of Al content. The partial substitution of Al by Zr improves both the reducibility and the dispersion of copper species as revealed by H₂-TPR results. The N₂O chemisorption and Cu K-edge XAFS results conformably indicate that the Cu species in CuZnAl_0.8Zr_0.2O possesses the highest dispersion. In addition, after used in DME SR reaction, the catalyst CuZnAl_0.8Zr_0.2O possesses the highest Cu⁺/Cu⁰ ratio, as calculated by Cu K-edge XANES fitting. The lowest CO selectivity during DME SR over this catalyst is highly related to the highest Cu⁺/Cu⁰ ratio.     

Mesoporous CexMn1−xO2 composites as novel alternative carriers of supported Co3O4 catalysts for CO preferential oxidation in H2 stream

The mesoporous Co₃O₄ supported catalysts on Ce–M–O (M = Mn, Zr, Sn, Fe and Ti) composites were prepared by surfactant-assisted co-precipitation with subsequent incipient wetness impregnation (SACP–IWI) method. The catalysts were employed to eliminate trace CO from H₂-rich gases through CO preferential oxidation (CO PROX) reaction. Effects of M type in Ce–M–O support, atomic ratio of Ce/(Ce + Mn), Co₃O₄ loading and the presence of H₂O and CO₂ in feed were investigated. Among the studied Ce–M–O composites, the Ce–Mn–O is a superior carrier to the others for supported Co₃O₄ catalysts in CO PROX reaction. Co₃O₄/Ce_0.9Mn_0.1O₂ with 25 wt.% loading exhibits excellent catalytic properties and the 100% CO conversion can be achieved at 125–200 °C. Even with 10 vol.% H₂O and 10 vol.% CO₂ in feed, the complete CO transformation can still be maintained at a wide temperature range of 190–225 °C. Characterization techniques containing N₂ adsorption/desorption, X-ray diffraction (XRD), H₂ temperature-programmed reduction (H₂-TPR) and scanning electron microscopy (SEM) were employed to reveal the relationship between the nature and catalytic performance of the developed catalysts. Results show that the specific surface area doesn’t obviously affect the catalytic performance of the supported cobalt catalysts, but the right M type in carrier with appropriate amount effectively improves the Co₃O₄ dispersibility and the redox behavior of the catalysts. The large reducible Co³⁺ amount and the high tolerance to reduction atmosphere resulted from the interfacial interaction between Co₃O₄ and Ce–Mn support may significantly contribute to the high catalytic performance for CO PROX reaction, even in the simulated syngas.     

Hydrogen production over Ni/ceria-supported catalysts by partial oxidation of methane

The catalytic performance of Ni dispersed on ceria-doped supports, (Ce_0.88La_0.12) O_2-x, (Ce_0.91Gd_0.09) O_2-x, (Ce_0.71Gd_0.29) O_2-x, (Ce_0.56Zr_0.44) O_2-x and pure ceria, was tested for the catalytic partial oxidation of Methane (CPOX). The catalysts were characterized by Brunauer Emmett Teller (BET), X-ray diffraction (XRD), temperature programmed reduction (TPR) and temperature programmed oxidation (TPO). Ni/ (Ce_0.56Zr_0.44) O_2-x showed higher Hydrogen production than the Ni/Gadolinium-doped catalysts, which may be due to its higher reducibility and surface area. By enhancing the support reducibility in Ni/doped-ceria catalysts, their catalytic activity is promoted because the availability of surface lattice oxygen is increased, which can participate in the formation of CO and H₂. It was also found that Ni/(Ce_0.56Zr_0.44) O_2-x showed higher catalytic performance after redox pretreatments. Similarly, a higher amount of H₂ or O₂ was consumed during hydrogenation and oxidation pretreatments, respectively. This may be correlated to re-dispersion of metallic particles and changes on the metal-support interface. In addition, it was observed that the ionic conductivity of Ni/(Ce_0.56Zr_0.44) O_2-x had an effect on the amount of carbon formed during the CPOX reaction at oxygen concentrations lower than the stoichiometric required, O/C ratios lower than 0.6. Its high oxygen mobility may have accelerated the surface oxidation reactions of carbon by reactive oxygen species, thus, inhibiting carbon growth on the catalyst surface.     

SrCe0.7Zr0.2Eu0.1O3-based hydrogen transport water gas shift reactor

Proton-transport-membrane water gas shift (WGS) reactors, based on thin dense SrCe_0.7Zr_0.2Eu_0.1O_3−δ membranes on tubular Ni–SrCe_0.8Zr_0.2O_3−δ supports, were developed to increase H₂ yields relative to thermodynamic limitations. Pure H₂ permeate, total H₂ production, and reactor side CO conversion and H₂/CO effluent ratio were measured as a function of temperature, flow rate, CO concentration and H₂O/CO feed ratios. CO conversion, total H₂ production and yield, and the H₂/CO in the reactor side effluent increased with increasing temperature and H₂O/CO feed ratios. CO conversions of 84% and 90% were achieved at 900 °C with H₂O/CO feed ratios of 1/1 and 2/1, respectively. These respective 77% and 44% increases in CO conversion compared to feed gas condition thermodynamics resulted in 73% and 42% increases in H₂ production. Permeated H₂ and total H₂ production increased with increasing flow rate and CO concentration. Finally, membrane stability under WGS conditions was significantly improved by Zr substitution.     

Formation of Ce0.8Sm0.2O1.9 nanoparticles by urea-based low-temperature hydrothermal process

The synthesis and formation mechanism of the nano-sized Ce_0.8Sm_0.2O_1.9 particles prepared by a urea-based low-temperature hydrothermal process was investigated in this study. From ex situ X-ray diffraction and induced coupled plasma-atomic emission spectroscopy investigations, it was found that large quantities of cerium hydroxide co-precipitated with some samarium hydroxide at the initial stage of the hydrothermal process. The remaining Sm³⁺ ions in the solutions were further hydrolyzed and deposited on the surface of the cerium hydroxide-rich precipitates to form a core–shell-like structure. During the hydrothermal process, the core–shell-like structure transformed to a single cubic fluorite phase which is due to the incorporation of the deposited samarium hydroxide into the cerium oxide-rich core. Further, the average grain size of the synthesized nanocrystalline Ce_0.8Sm_0.2O_1.9 was reduced with increasing the urea concentration in the solution. The density of the disk prepared with the synthesized Ce_0.8Sm_0.2O_1.9 powders was found to increase with a decrease in the grain size of Ce_0.8Sm_0.2O_1.9. The existence of SO₄²⁻ anions in the SDC powders prepared at low-urea concentration may result in the SDC disks with low density due to their decomposition during sintering process.     

Catalytic conversion of CH4 and CO2 to synthesis gas on Ni/SiO2 catalysts containing Gd2O3 promoter

A series of Ni/SiO₂ catalysts containing different amounts of Gd₂O₃ promoter was prepared, characterized by H₂-adsorption and XRD, and used for carbon dioxide reforming of methane (CRM) and methane autothermal reforming with CO₂ + O₂ (MATR) in a fluidized-bed reactor. The results of pulse surface reactions showed that Ni/SiO₂ catalysts containing Gd₂O₃ promoter could increase the activity for CH₄ decomposition, and Raman analysis confirmed that reactive carbon species mainly formed on the Ni/SiO₂ catalysts containing Gd₂O₃ promoter. In this work, it was found that methane activation and reforming reactions proceeded according to different mechanisms after Gd₂O₃ addition due to the formation of carbonate species. In addition, Ni/SiO₂ catalysts containing Gd₂O₃ promoter demonstrated higher activity and stability in both CRM and MATR reactions in a fluidized bed reactor than Ni/SiO₂ catalysts without Gd₂O₃ even at a higher space velocity.     

Catalytic behavior of Ni/ZrxTi1−xO2 and the effect of SiO2 doping in oxidative steam reforming of n-butane

Catalytic behaviors of TiO₂-, Zr_0.5Ti_0.5O₂-, and ZrO₂-supported Ni catalysts were investigated for oxidative steam reforming of n-C₄H₁₀ at 723 K. The composite oxide support, Zr_0.5Ti_0.5O₂, shows high specific surface area (136 m²/g), leading to fine Ni particles. Thus, the Ni/Zr_0.5Ti_0.5O₂ catalyst exhibits higher and more stable activity than that exhibited by other catalysts. However, relatively large amounts of coke are deposited on the catalyst during reaction. Thus, to retard carbon deposition, the influence of SiO₂ additive was studied. Large amounts of SiO₂ additive (5 or 10 mol%) decrease initial activity; at 10 mol%, degradation is also induced by oxidation of Ni⁰. However, small amounts of SiO₂ additive (1.5 mol%) effectively retard coking without lowering initial activity. The resultant Ni/Zr_0.5Ti_0.5O₂–SiO₂ (1.5 mol%) catalyst exhibits high and stable activity without coking.     

Nickel zirconia cerate cermet for catalytic partial oxidation of ethanol in a solid oxide fuel cell system

Ni + Ce_xZr_1−xO₂ (x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0) cermets were synthesized and their catalytic performance for partial oxidation of ethanol (POE) reaction was studied. The structure, reducibility properties and carbon deposition behavior of the various catalysts were investigated. Among the various catalysts, Ni + Ce_0.8Zr_0.2O₂ displayed the best catalytic activity in terms of H₂ selectivity and also the highest coking resistance. The fuel cell with Ni + Ce_0.8Zr_0.2O₂ catalyst layer delivered a peak power density of 692 mW cm⁻² at 700 °C when operating on ethanol–O₂ gas mixtures, comparable to that applying hydrogen fuel. The fuel cell also showed an improved operation stability on ethanol–O₂ fuel for 150 h at 700 °C. Ni + Ce_0.8Zr_0.2O₂ is promising as an active and coke-tolerant catalyst layer for solid oxide fuel cells operating on ethanol-O₂ fuel, which makes it highly attractive by applying biofuel in an SOFC system for efficiency electric power generation.