Structured catalysts for the conversion of liquefied petroleum gas to hydrogen-rich gas and for anode off-gas afterburning

A number of mixed oxide Ce_0.75Zr_0.25O₂ supports were prepared, tested for reproducibility, and characterized by physicochemical methods. The most reproducible preparation method was adapted for depositing the mixed oxide on a FeCrAlloy mesh substrate coated by a protective alumina layer. Based on the obtained structured Ce_0.75Zr_0.25O₂/θ-Al₂O₃/FeCrAl support, the Rh/Ce_0.75Zr_0.25O₂/Al₂O₃/FeCrAl and Pt/Ce_0.75Zr_0.25O₂/Al₂O₃/FeCrAl catalysts were prepared and tested in the reactions of partial oxidation of LPG and deep oxidation of anode gases, respectively. Rh/Ce_0.75Zr_0.25O₂/Al₂O₃/FeCrAl provided complete conversion of LPG into synthesis gas of a composition close to the equilibrium one. Pt/Ce_0.75Zr_0.25O₂/Al₂O₃/FeCrAl provided complete conversion of all components of the anode gases at GHSV = 20,000–40,000 h⁻¹; however, at higher GHSV values, methane conversion decreased. The studies on the effect of methane content on deep oxidation of anode off gases showed that methane conversion began to decrease at a 1.5-fold excess of methane and dropped to 50% at a 10-fold excess of methane.     

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.     

Enhanced low-temperature activity for CO2 methanation over Ru doped the Ni/CexZr(1−x)O2 catalysts prepared by one-pot hydrolysis method

A series of 30 wt%Ni/Ce_xZr_1?xO₂ catalysts doped with Ru ranging from 0 to 5 wt% were prepared by one-pot hydrolysis of metal nitrates with ammonium carbonate for carbon dioxide methanation at low temperature range of 150–310 °C. The influences of Ce/Zr molar ratios and Ru contents on the physicochemical properties and catalytic activities of prepared catalysts were systematically investigated. The addition Ru can improve the Ni dispersion and the basicity of the yRu-30Ni/Ce_0.9Zr_0.1O₂ catalysts surface. As a result, their low-temperature catalytic activity had been enhanced over these doped Ru promoted catalysts. The optimal catalyst was 3Ru-30Ni/Ce_0.9Zr_0.1O₂ on which the CO₂ conversion reached theoretical equilibrium value as high as 98.2% with the methane selectivity of 100% at a reaction temperature as low as 230 °C. Moreover, there was almost no deactivation for the 3Ru-30Ni/Ce_0.9Zr_0.1O₂ catalyst during 300 h at 230 °C indicating excellent catalytic stability and coke resistence ability. It was also found that the low-temperature activity of 3Ru-30Ni/Ce_0.9Z_r0.1O₂ catalyst prepared by one-pot hydrolysis method was much higher than the one prepared by impregnation method.     

Low temperature hydrogen production by catalytic steam reforming of methane in an electric field

Catalytic steam reforming of methane in an electric field (electroreforming) at low temperatures such as 423 K was investigated. Pt catalysts supported on CeO₂, Ce_xZr_1−xO₂ solid solution and a physical mixture of CeO₂ and other insulators (ZrO₂, Al₂O₃ or SiO₂) were used for electroreforming. Among these catalysts, Pt catalyst supported on Ce_xZr_1−xO₂ solid solution showed the highest activity for electroreforming (CH₄ conv. = 40.6% at 535.1 K). Results show that the interaction among the electrons, metal loading, and catalyst support was important for high catalytic activity on the electroreforming. Catalytic activity of the electroreforming increased in direct relation to the input current. Characterizations using X-ray diffraction (XRD), temperature programmed reduction with H₂ (H₂-TPR), and alternate current (AC) impedance measurement show that the catalyst structure is an important factor for activity of electroreforming.     

Effect of catalyst preparation on Au/Ce1−xZrxO2 and Au–Cu/Ce1−xZrxO2 for steam reforming of methanol

We tested 3 wt% gold (Au) catalysts on CeO₂–ZrO₂ mixed oxides, prepared by co-precipitation (CP) and the sol–gel (SG) technique, for steam reforming of methanol (SRM). Uniform Ce_1−xZr_xO₂ solid solution was dependent on the Zr/Ce ratio, where the incorporation of Zr⁴⁺ into the Ce⁴⁺ lattice with a ratio of 0.25 resulted in smaller ceria crystallites and better reducibility, and was found to be efficient for SRM activity. The catalytic activity was suppressed when the ratio was ≥0.5, which led to the segregation of Zr from solid solution and sintering of Au nanoparticles. It was found that the CP technique produced better catalysts than SG in this case. For the bimetallic catalysts, the co-operation of Au–Cu supported on Ce_0.75Zr_0.25O₂ (CP) exhibited superior activities with complete methanol conversion and low CO concentration at 350 °C. Furthermore, the size of the alloy particle was strongly dependent on the pH level during preparation.     

Rh- and Rh–Ni–MgO-based structured catalysts for on-board syngas production via gasoline processing

Rh/Ce_0.75Zr_0.25O_2-δ-ƞ-Al₂O₃/FeCrAl and Rh/Ni–MgO/Ce_0.75Zr_0.25O_2-δ-ƞ-Al₂O₃/FeCrAl FeCrAlloy wire mesh supported catalysts were prepared via multistep procedure. They were characterized by XRD, SEM and TEM techniques. A comparative study of autothermal reforming (ATR) of isooctane and simulated gasoline (blends of isooctane, ortho-xylene and naphthalene) over Rh/Ce_0.75Zr_0.25O_2-δ-ƞ-Al₂O₃/FeCrAl and Rh/Ni–MgO/Ce_0.75Zr_0.25O_2-δ-ƞ-Al₂O₃/FeCrAl was performed. Both catalysts showed excellent performance in ATR of isooctane at molar ratios of O₂:C = 0.51 and H₂O:C = 2.59, T = 750°С and GHSV = 10000 h⁻¹. In the ATR of isooctane – o-xylene blend in presence of Rh–Ni-containing catalyst carbon formation was observed. Rh-containing catalyst demonstrated rather good activity and stability even in the case of isooctane – o-xylene – naphthalene blend.     

Synthesis of flowerlike ceria–zirconia solid solution for promoting dry reforming of methane

Using a newly developed two-step hydrothermal process, flowerlike Ce_0.5Zr_0.5O₂ with an oxygen storage capacity (OSC) of 536 μmol O₂ g^?1, almost twice as high as that of pure flowerlike CeO₂ (284 μmol O₂ g^?1), can be synthesized. The synthesized ceria-based oxide supports loaded with Ni are dispersed in a ceramic fiber network to form paper-structured catalysts (PSCs). Among the prepared PSCs, the PSC with the flowerlike Ce_0.5Zr_0.5O₂ exhibits the highest catalytic performance for dry reforming of methane (DRM) at 750 °C with the initial methane conversion of 88.4%, degradation rate of 0.1% h^?1 and amount of deposited carbon of 0.04 g per gram catalyst, whereas for the Ce_0.5Zr_0.5O₂ synthesized by the one-step hydrothermal process, the values are 83.7%, 0.62% h^?1 and 0.07 g per gram catalyst, respectively. This is attributed to the Ni anti-sintering on the petals of the flowerlike structure and the coking tolerance resulting from the high OSC.     

Deoxygenation of oleic acid over Ce(1–x)Zr(x)O2 catalysts in hydrogen environment

Ce_(1–x)Zr_(x)O₂ catalysts were prepared by co-precipitation method for deoxygenation (DO) of oleic acid. The CeO₂/ZrO₂ ratio was systematically varied to optimize Ce_(1–x)Zr_(x)O₂ catalysts. Ce_0.6Zr_0.4O₂ exhibited the highest oleic acid conversion as well as high selectivity to C₉ ∼ C₁₇ compounds (diesel fuel range) at the reaction temperature of 300 °C. The high activity/selectivity of Ce_0.6Zr_0.4O₂ catalyst was correlated to its reducibility, oxygen storage capacity and crystallite size.     

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.     

Hydrogen production by autothermal reforming of methane over NiPd catalysts: Effect of support composition and preparation mode

NiPd/Ce_0.5Zr_0.5O₂/Al₂O₃ and NiPd/La₂O₃/Ce_0.5Zr_0.5O₂/Al₂O₃ catalysts were prepared by incipient wetness co-impregnation method or sequential impregnation method for autothermal reforming of methane (ATR of CH₄). The influence of the preparation mode, Ce_0.5Zr_0.5O₂ and La₂O₃ additives on the physicochemical properties of NiPd supported catalysts and the effect on their activity to produce hydrogen by ATR of CH₄ were investigated. Characterization of fresh and spent Ni-based catalysts by X-ray fluorescence spectroscopy, N₂ adsorption, X-ray diffraction, H₂ temperature-programmed reduction, high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy were performed. It was demonstrated that support composition determines NiO dispersion as well as reducibility of Ni species through different strength of Ni-support interaction. The preparation method modifies the phase composition and catalyst ability for reduction. The catalyst evolution under reaction conditions was studied. The NiO (∼15 nm) and NiPd alloy (∼18 nm) phases were observed in the spent catalysts. It was found that the Ni^o/NiO ratio can be regulated by support composition and preparation mode of catalysts. It is demonstrated that studied catalysts provide high methane conversion of 90–100%, CO yield of 55–85% and H₂ yield of 55–75% in ATR of CH₄ at 750–950 °C. The optimal composition and preparation method of catalyst were selected. The best ATR of CH₄ performance is provided by 10 Ni_0.5Pd/10Ce_0.5Zr_0.5O₂/Al₂O₃ catalyst prepared by Pd/Ni sequential impregnation method that can be associated with peculiarity of NiPd particles structure and the optimal ratio between NiO species with different ability for reduction.     

Powder and structured Pt/Ce0.75Zr0.25O2-based catalysts: Water gas shift performance and quasi in situ XPS studies

The data on the performance in water gas shift reaction of a powder 5 wt% Pt/Ce_0.75Zr_0.25O₂ and a structured 0.33 wt% Pt/Ce_0.75Zr_0.25O₂/θ-Al₂O₃/FeCrAl catalysts are reported in this work. For the powder one the lowest outlet CO concentrations were shown to be 0.5, 0.9 and 1.5 vol% corresponding to the initial ones of 5, 10 and 15 vol%, respectively; the temperature required to reach these values did not exceed 310 °C. The quasi in situ XPS data have shown that doping CeO₂ with Zr enhances the reducibility of the oxide allowing Ce³⁺ formation without any treatment. Additionally, it was found that there are 20–30% of nonmetallic Pt atoms on the surface even after a treatment in CO at 300 °C. For the structured catalyst the downward temperature gradient along the monolith was observed with a dispersion of 50–60 °C. The lowest CO concentrations were observed at the temperatures at the catalyst's back point of 280 °C–3.9 and 4.3 vol% CO in the dry gas for 15,700 and 31,400 cm³·g_cat⁻¹·h⁻¹, respectively, for 10 vol% CO in the feed gas.     

Hydrogen production through autothermal reforming of CH4: Efficiency and action mode of noble (M = Pt,Pd) and non-noble (M = Re,Mo, Sn) metal additives in the composition of Ni-M/Ce0.5Zr0.5O2/Al2O3 catalysts

Hydrogen production through autothermal reforming of methane (ATR of CH₄) over promoted Ni catalysts was studied. The control of the ability to self-activation and activity of Ni-M/Ce_0.5Zr_0.5O₂/Al₂O₃ catalysts was achieved by tuning their reducibility through the application of different types (M = Pt, Pd, Re, Mo or Sn) and content (molar ratio M/Ni = 0.003, 0.01 or 0.03) of additive. The comparison of the efficiency and action mode of noble (M = Pt, Pd) and non-noble (M = Re, Mo, Sn) metal additives in the composition of Ni-M/Ce_0.5Zr_0.5O₂/Al₂O₃ catalysts was performed using X-ray fluorescence analysis, N₂ adsorption, X-ray diffraction, high-resolution transmission electron microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, temperature-programmed reduction with hydrogen, and thermal analysis. The composition-characteristics-activity correlations were determined. It was shown that the introduction of a promoter does not affect the textural and structural properties of catalysts but influences their reducibility and performance in ATR of CH₄. At the similar dispersion of NiO active component (11 ± 2 nm), the Ni²⁺ reduction is intensified in the following order of additives: Mo < Sn < Re ≤ Pd < Pt. It was found that for the activation of Ni and Ni–Sn catalysts before ATR of CH₄ tests, the pre-reduction is required. On the contrary, the introduction of Pt, Pd and Re additives leads to the self-activation of catalysts under the reaction conditions and an increase of the H₂ yield due to the enhanced reducibility of Ni²⁺. The efficient and stable catalyst for hydrogen production has been developed: in ATR of CH₄ at 850 °C over an optimum 10Ni-0.9Re/Ce_0.5Zr_0.5O₂/Al₂O₃ catalyst the H₂ yield of 70% is attained. The designed catalyst has enhanced stability against oxidation and sintering of Ni active component as well as high resistance to coking.     

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.     

A new nickel–ceria composite for direct-methane solid oxide fuel cells

Various Ni–La_xCe_1−xO_y composites were synthesized and their catalytic activity, catalytic stability and carbon deposition properties for steam reforming of methane were investigated. Among the catalysts, Ni–La_0.1Ce_0.9O_y showed the highest catalytic performance and also the best coking resistance. The Ni–La_xCe_1−xO_y catalysts with a higher Ni content were further sintered at 1400 °C and investigated as anodes of solid oxide fuel cells for operating on methane fuel. The Ni–La_0.1Ce_0.9O_y anode presented the best catalytic activity and coking resistance in the various Ni–La_xCe_1−xO_y catalysts with different ceria contents. In addition, the Ni–La_0.1Ce_0.9O_y also showed improved coking resistance over a Ni–SDC cermet anode due to its improved surface acidity. A fuel cell with a Ni–La_0.1Ce_0.9O_y anode and a catalyst yielded a peak power density of 850 mW cm⁻² at 650 °C while operating on a CH₄–H₂O gas mixture, which was only slightly lower than that obtained while operating on hydrogen fuel. No obvious carbon deposition or nickel aggregation was observed on the Ni–La_0.1Ce_0.9O_y anode after the operation on methane. Such remarkable performances suggest that nickel and La-doped CeO₂ composites are attractive anodes for direct hydrocarbon SOFCs and might also be used as catalysts for the steam reforming of hydrocarbons.     

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.     

Effect of Co,Fe and Rh addition on coke deposition over Ni/Ce0.5Zr0.5O2 catalysts for steam reforming of ethanol

Ni-based monometallic and bimetallic catalysts (Ni, NiRh, NiCo and NiFe) supported on Ce_0.5Zr_0.5O₂ support were evaluated on the steam reforming of ethanol (SRE) performance. The supports of Ce_0.5Zr_0.5O₂ composite oxide was prepared by co-precipitation method with Na₂CO₃ precipitant and assigned as CeZr(N). The monometallic catalyst was prepared by incipient wetness impregnation method and assigned as Ni/CeZr(N). The bimetallic catalysts were prepared by co-impregnation method to disperse the metals on the CeZr(N) support and assigned as NiM/CeZr(N). All samples were characterized by using XRD, TPR, BET, EA and TEM techniques at various stages of the catalyst. The results indicated that the facile reduction and smaller particle size of Ni/CeZr(N) (T₉₉ = 300 °C) and NiRh/CeZr(N) (T₉₉ = 250 °C) catalysts were preferential than the NiFe/CeZr(N) (T₉₉ = 325 °C) and NiCo/CeZr(N) (T₉₉ = 375 °C) catalysts. Also, both the Ni/CeZr(N) and NiRh/CeZr(N) catalysts displayed better durability among these catalysts over 100 h and 400 h, respectively. Since the serious coke formation for the NiCo/CeZr(N) catalyst, the activity only maintained around 6 h, the durability on the NiFe/CeZr(N) catalyst approached 50 h.     

Hydrogen production from the oxidative steam reforming of methanol over AuCu nanoparticles supported on Ce1-xZrxO2 in a fixed-bed reactor

Oxidative steam reforming of methanol over monometallic gold (Au) and bimetallic Au-copper (Cu) supported on ceria-zirconia (CeO₂ZrO₂) was examined over the temperature range of 200–400 °C in a fixed-bed reactor. The composition of CeO₂ZrO₂ supports was also studied for their catalytic activity. The Au/Ce_0.75Zr_0.25O₂ catalyst exhibited the highest methanol (CH₃OH) conversion level (96.7%) and hydrogen (H₂) yield (59.7%) due to the formation of a homogeneous Ce_1-xZr_xO₂ solid solution. When Cu was introduced in the Au catalysts, all of the bimetallic catalysts presented a better stability for CH₃OH conversion as well as H₂ yield in comparison to the monometallic catalysts, which was due to the partial electron transfer from Cu to Au metals. The performance of the AuCu/Ce_0.75Zr_0.25O₂ catalysts, which was evaluated under identical conditions, was ranked in the order: 3Au1Cu > 1Au3Cu > 1Au1Cu.     

Effect of ZrO2 on the performance of Co–CeO2 catalysts for hydrogen production from waste-derived synthesis gas using high-temperature water gas shift reaction

In this study, highly active and stable CeO₂, ZrO₂, and Zr_(1-x)Ce_(x)O₂-supported Co catalysts were prepared using the co-precipitation method for the high-temperature water gas shift reaction to produce hydrogen from waste-derived synthesis gas. The physicochemical properties of the catalysts were investigated by carrying out Brunauer-Emmet-Teller, X-ray diffraction, CO-chemisorption, Raman spectroscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and H₂-temperature-programmed reduction measurements. With an increase in the ZrO₂ content, the surface area and reducibility of the catalysts increased, while the interaction between Co and the support and the dispersion of Co deteriorated. The Co–Zr_0.4Ce_0·6O₂ and Co–Zr_0.6Ce_0·4O₂ catalysts showed higher oxygen storage capacity than that of the others because of the distortion of the CeO₂ structure due to the substitution of Ce⁴⁺ by Zr⁴⁺. The Co–Zr_0.6Ce_0·4O₂ catalyst with high reducibility and oxygen storage capacity exhibited the best catalytic performance and stability among all the catalysts investigated in this study.     

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.     

High-surface-area Ce0.8Zr0.2O2 solid solutions supported Ni catalysts for ammonia decomposition to hydrogen

Three kinds of Ce_0.8Zr_0.2O₂ solid solutions synthesized via surfactant-assisted route, co-precipitation, and sol–gel method were used as supports of Ni-based catalysts by impregnation. Their catalytic activities in ammonia decomposition to hydrogen were tested, and the structural effect of support and the influence of nickel content on catalytic activity were evaluated. Mesoporous/high-surface-area Ce_0.8Zr_0.2O₂ support synthesized by surfactant-assisted method exhibited better promoting effect than other supports when the same content of Ni was loaded. The interactions between Ni species and Ce_0.8Zr_0.2O₂ supports were found to greatly affect the chemical properties of catalysts, including redox, H₂ adsorption, and catalysis. The promoting effects of Ce in catalysts, plentiful vacancies in the solid solutions due to the doping of Zr⁴⁺, and high surface areas of the supports were discussed on the ammonia decomposition activities of the resultant catalysts, as well as the influence of hydrogen spillover. The ammonia conversion of 95.7% with the H₂ producing rate of 89.3 mL/min·g_cat was achieved at 550 °C over the Ni catalysts supported on the mesoporous/high-surface-area Ce_0.8Zr_0.2O₂.