Properties of Ni/Y2O3 and its catalytic performance in methane conversion to syngas

Ni/Y₂O₃, with Y₂O₃ support prepared by the conventional precipitation method, was prepared by an impregnation method. The physicochemical properties of Y₂O₃ and Ni/Y₂O₃ were characterized by BET, CO₂-TPD, NH₃-TPD, TPR, XRF and TGA, and compared with those of γ-Al₂O₃ and Ni/γ-Al₂O_3, respectively. The catalytic performance of Ni/Y₂O₃ in the reaction of partial oxidation of methane (POM) to syngas was evaluated and compared with that of Ni/γ-Al₂O₃ catalyst, too. The results showed that, Y₂O₃ was a basic support with few acidic sites while γ-Al₂O₃ was an acidic support. NiO particles supported on Y₂O₃ were more easily to be reduced than those supported on γ-Al₂O₃. In the partial oxidation of methane, Ni/Y₂O₃ catalyst showed high catalytic activity and exhibited better catalytic stability than Ni/γ-Al₂O₃. After POM reaction at 700 °C for 550 h, methane conversion decreased little and only 2.2 wt% carbon was deposited on Ni/Y₂O₃ catalyst. Ni/Y₂O₃ was stable in POM even after a series of reaction temperature variations within the temperature range of 400 ∼ 800 °C.     

Hydrogen generation from Al-Water reaction promoted by M-B/γ-Al2O3 (M = Co,Ni) catalyst

Al-water reaction promoted by catalysts is a promising hydrogen generation technology. In this work, a high-activity M-B/γ-Al₂O₃ (M = Co, Ni) catalyst is prepared by wet chemical reduction method. It is found that M-B/γ-Al₂O₃ catalyst significantly promotes the Al-water reaction and decreases the induction time. When the molar ratio of γ-Al₂O₃ to Co-M in Co–B/γ-Al₂O₃ catalyst is 1:1, the induction time is only 0.43 h. The catalytic activity of M-B/γ-Al₂O₃ is proportional to its active area. SEM analyses show that M-B particles are dispersed on γ-Al₂O₃ surface, which reduces the agglomeration of M-B and increases the active surface of M-B/γ-Al₂O₃, leading to a high catalytic activity. A possible mechanism is proposed, which shows that the dissociation of water molecules on γ-Al₂O₃ surface and the microgalvanic interaction between M-B and Al can promote the hydration process of passive oxide film on Al particle surface, speeding up the Al-water reaction.     

Mesocellular-foam-silica-supported Ni catalyst: Effect of pore size on H2 production from cellulose pyrolysis

Supported nickel metal can be used as a tar-cracking catalyst in the thermal processing of large organics to give H₂. Though porous supports offer the opportunity to disperse a relatively large amount of nickel, catalytic sites within small pores may be inaccessible to large tar molecules. To investigate this, we prepared nickel catalysts supported on γ-Al₂O₃ and on SBA-15- and mesocellular-foam-(MCF)-type silicas and studied their catalytic activities in the pyrolytic decomposition of cellulose (RT → 800 °C, ∂T/∂t = 40 °C/min). A thermogravimetric analyser-mass spectrometer (TG-MS) was used to study the influence of the Ni catalyst and support materials on the H₂ yield and selectivity. The silica-MCF-supported Ni catalyst decreased char residue and enhanced H₂ yield, producing 1.6 and 3.5× the H₂ yield obtained using SBA-15-supported Ni and γ-Al₂O₃-supported Ni, respectively. MCF, with ultra-large pores (d ∼ 15−50 nm), was thus identified as the most beneficial catalyst support for this application.     

Pre-reforming of liquefied petroleum gas over nickel catalysts supported on magnesium aluminum mixed oxides

A series of Ni/Mg_xAl catalysts with different Mg/Al molar ratios were prepared by impregnating Mg-Al mixed oxides with nickel nitrate aqueous solution and used for the pre-reforming of LPG in the temperature range of 400-500 °C. XRD and H₂-TPR results showed that the Ni/Mg_xAl catalysts calcined at 800 °C mainly consisted of γ-Al₂O₃, Mg(Ni)Al₂O₄ and Mg(Ni)O phases varying with Mg/Al molar ratio without free NiO species observed. The effects of Mg/Al molar ratio, S/C molar ratio and reaction temperature on the catalytic behavior of the Ni/Mg_xAl catalysts were investigated in detail. The results revealed that the catalyst with Mg/Al molar ratio of 1.25 had the highest catalytic activity and stability. The increase in S/C molar ratio promoted both the steam reforming of LPG and the methanation of carbon oxides and hydrogen. The stability tests of 15%Ni/Mg_1.25Al catalyst showed that the catalyst was stable for the pre-reforming of LPG, and the stability decreased with elevating the reaction temperature due to more coke deposition.     

Screening of supported transition metal catalysts for hydrogen production from glucose via catalytic supercritical water gasification

In total 17 heterogeneous catalysts, with combinations of 4 transition metals (Ni, Ru, Cu and Co) and various promoters (e.g., Na, K, Mg, or Ru) supported on different materials (γ-Al₂O₃, ZrO₂, and activated carbon (AC)), were investigated with respect to their catalytic activity and stability for H₂ production from glucose via supercritical water gasification (SCWG). The experiments were carried out at 600 °C and 24 MPa in a bench-scale continuous-flow tubular reactor. Ni (in metallic form) and Ru (in both metallic and oxidized forms) supported on γ-Al₂O₃ exhibited very high activity and H₂ selectivity among all of the catalysts investigated for a time-on-stream of 5-10 h. With Ni20/γ-Al₂O₃ (i.e., γ-Al₂O₃ with 20 wt% Ni), a H₂ yield of 38.4 mol/kg glucose was achieved, approximately 20 times higher than that obtained during the blank test without catalyst (1.8 mol/kg glucose). In contrast, Cu and Co catalysts were much less effective for glucose SCWG reactions. As for the effects of catalyst support materials on activity, the following order of sequence was observed: γ-Al₂O₃ > ZrO₂ > AC. In addition, Mg and Ru were found to be effective promoters for the Ni/γ-Al₂O₃ catalyst, suppressing coke and tar formation.     

Support and alloy effects on activity and product selectivity for ethanol steam reforming over supported nickel cobalt catalysts

Ni, Co and bimetallic Ni–Co catalysts supported on Ca-γ-Al₂O₃ and ZrO₂ were investigated for the production of hydrogen via ethanol steam reforming (ESR). Catalysts were prepared by wet impregnation method and characterized using temperature-programmed reduction (TPR), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). ESR and temperature-programmed desorption of ethanol (ethanol-TPD) were carried out in a continuous flow fixed bed micro-reactor and the outlet gases were monitored by an on-line GC or MS. Ni is found to be more active for the C–C bond rupture than Co on both supports, Ca-γ-Al₂O₃ and ZrO₂. Catalyst support plays very important roles for the ESR. Strong interaction between support and metal affects the formation of NiCo bimetallic compound, resulting in the variety of catalytic activity. On Ca-γ-Al₂O₃ support, the catalytic activity of ESR follows the sequence of 10%Ni > 6.7%Ni 3.3%Co ∼ 3.3%Ni 6.7%Co > 10%Co. On ZrO₂, the trend is 10%Ni > 6.7%Ni 3.3%Co > 10%Co > 3.3%Ni 6.7%Co. The H₂O adsorption/activation ability of the support determines the reaction pathway and thus the product selectivity. On Ca-γ-Al₂O₃, water gas shift reaction is more favorable than on ZrO₂, due to the availability of surface OH groups. The roles of the metal and support for ESR are also discussed.     

Hydrogen-rich syngas production by catalytic cracking of tar in wastewater under supercritical condition

This paper presents the results from experimental study of syngas production by catalytic cracking of tar in wastewater under supercritical condition. Ni/Al₂O₃ catalysts were prepared via the ultrasonic assisted incipient wetness impregnation on activated alumina, and calcined at 600 °C for 4 h. All catalysts showed mesoporous structure with specific surface area in a range of 146.6–215.3 m²/g. The effect of Ni loading (5–30 wt%), reaction temperature (400–500 °C), and tar concentration (0.5–7 wt%) were systematically investigated. The overall reaction efficiency and the gas yields, especially for H₂, were significantly enhanced with an addition of Ni/Al₂O₃ catalysts. With 20%Ni/Al₂O₃, the H₂ yield increased by 146% compared to the non-catalytic experiment. It is noteworthy that the reaction at 450 °C with the addition of 20%Ni/Al₂O₃ had a comparable efficiency to the reaction without catalyst at 500 °C. The maximum H₂ yield of 46.8 mol/kg_tar was achieved with 20%Ni/Al₂O₃ at 500 °C and 0.5 wt% tar concentration. The catalytic performance of the catalysts gradually decreased as the reuse cycle increased, and could be recovered to 88% of the fresh catalyst after regeneration. 20%Ni/Al₂O₃ has a potential to improve H₂ production, as well as a good reusability. Thus, it is considered a promising catalyst for energy conversion of tar in wastewater.     

Hydrogen production by steam reforming of liquefied natural gas (LNG) over nickel catalysts supported on cationic surfactant-templated mesoporous aluminas

Two types of mesoporous γ-aluminas (denoted as A-A and A-S) are prepared by a hydrothermal method under different basic conditions using cationic surfactant (cetyltrimethylammonium bromide, CTAB) as a templating agent. A-A and A-S are synthesized in a medium of ammonia solution and sodium hydroxide solution, respectively. Ni/γ-Al₂O₃ catalysts (Ni/A-A and Ni/A-S) are then prepared by an impregnation method, and are applied to hydrogen production by steam reforming of liquefied natural gas (LNG). The effect of a mesoporous γ-Al₂O₃ support on the catalytic performance of Ni/γ-Al₂O₃ is investigated. The identity of basic solution strongly affects the physical properties of the A-A and A-S supports. The high surface-area of the mesoporous γ-aluminas and the strong metal–support interaction of supported catalysts greatly enhance the dispersion of nickel species on the catalyst surface. The well-developed mesopores of the Ni/A-A and Ni/A-S catalysts prohibit the polymerization of carbon species on the catalyst surface during the reaction. In the steam reforming of LNG, both Ni/A-A and Ni/A-S catalysts give better catalytic performance than the nickel catalyst supported on commercial γ-Al₂O₃ (Ni/A-C). In addition, the Ni/A-A catalyst is superior to the Ni/A-S catalyst. The relatively strong metal–support interaction of Ni/A-A catalyst effectively suppresses the sintering of metallic nickel and the carbon deposition in the steam reforming of LNG. The large pores of the Ni/A-A catalyst also play an important role in enhancing internal mass transfer during the reaction.     

Hydrogen production from catalytic supercritical water reforming of glycerol with cobalt-based catalysts

Glycerol reforming under catalytic supercritical water at temperatures in the range of 723–848 K using Co catalyst deposited on various supports including ZrO₂, yttria-stabilized zirconia (YSZ), La₂O₃, γ-Al₂O₃, and α-Al₂O₃ was investigated. An increase in operating temperature promoted the continued increase in glycerol conversion; however, carbon formation causing system operation failure was observed for γ-Al₂O₃ and α-Al₂O₃ at high operating temperatures (i.e. 748–798 K). Co supported on YSZ provided the most efficient performance for hydrogen production. 10 wt.% Co loading on YSZ support was an optimum amount to enhance the reaction. The increase in glycerol conversion and reduction of the amount of liquid products were observed for lower weight hourly space velocity (WHSV), higher operating temperature or higher cobalt loading. On Co/YSZ catalyst, glycerol conversion of 0.94 and hydrogen yield of 3.72 was obtained with WHSV of 6.45 h⁻¹at 773 K.     

Coke-resistance enhancement of mesoporous γ-Al2O3 and MgO-supported Ni-based catalysts for sustainable hydrogen generation via steam reforming of acetic acid

Highly ordered mesoporous γ-Al₂O₃ particles and MgO materials were synthesized by evaporation induced self-assembly (EISA) and template-free hydrothermal co-precipitation routes, respectively. Ni, Ni–MgO, and Ni–La₂O₃-containing catalysts were prepared using a wet-impregnation method. The synthesized catalysts were characterized by N₂ adsorption–desorption, XRD, SEM-EDS, DRIFTS, XPS, TGA-DTA, and Raman spectroscopy analysis. The mesoporous γ-Al₂O₃ catalyst support exhibited a high surface area of 245 m²/g and average pore volume of 0.481 cm³/g. The DRIFTS results indicate the existence of large Lewis's acid regions in the pure γ-Al₂O₃ and metal-containing catalysts. Catalytic activity tests of pure materials and metal-containing catalysts were carried out at the reaction temperature of 750 °C and a feed molar ratio of AA/H₂O/Ar:1/2.5/2 over 3 h. Complete conversion of acetic acid and 81.75% hydrogen selectivity were obtained over the catalyst 5Ni@γ-Al₂O₃. The temperature and feed molar ratio had a noticeable impact on H₂ selectivity and acetic acid conversion. Increasing the water proportion in the feed composition from 2.5 to 10 considerably improved the catalytic activity by increasing hydrogen selectivity from 81.75% to 91%. Although the Ni-based γ-Al₂O₃-supported catalysts exhibited higher activity performance compared to the Ni-based MgO-supported catalysts, they were not as resistant to coke formation as were MgO-supported catalysts. The introduction of MgO and La₂O₃ into the Ni@γ-Al₂O₃ and Ni@MgO catalysts' structures played a significant role in lowering the carbon formation (from 37.15% to 17.6%–12.44% and 12.17%, respectively) and improving the thermal stability of the catalysts by decreasing the agglomeration of acidic sites and reinforcing the adsorption of CO₂ on the catalysts' surfaces. Therefore, coke deposition was reduced, and catalyst lifetime was improved.     

Alumina supported nano-platinum on copper nanoparticles prepared via galvanic displacement reaction for preferential carbon monoxide oxidation in presence of hydrogen

Improved catalytic centres with a minimum mass-loading of expensive platinum (Pt) have been anticipated for various catalytic applications, for instance preferential oxidation (PROX) of carbon monoxide (CO) in the presence of Hydrogen. Here, we report the synthesis of nano-Pt on the surface of copper (Cu) nanoparticles (NPs) supported on γ-Al₂O₃ (Pt_n(Cu)/γ-Al₂O₃) via galvanic displacement reaction (GDR) for the catalytic CO-PROX reaction. Pt_n(Cu)/γ-Al₂O₃ showed much improved CO-PROX performance compared to that of the as-synthesized Pt_l(Cu)/γ-Al₂O₃ catalyst. Importantly, no significant conversion of hydrogen at a lower temperature range (<200 °C) is observed during the CO-PROX reaction which is one of the essential prerequisites for the CO-PROX reaction. Moreover, Pt_n(Cu)/γ-Al₂O₃ showed the durable, long-term catalytic CO-PROX performance for 120 h. These results infer that realization of nano-Pt on the surface of the Cu NPs holds the promise as the catalytic centres with the minimum mass-loading of Pt for the CO-PROX reaction.     

Hydrothermal stability improvement of NiPt-containing γ-Al2O3 catalysts tested in aqueous phase reforming of glycerol/water mixture for H2 production

The hydrothermal stability of Ni and NiPt-containing γ-Al₂O₃ catalysts in aqueous phase reforming (APR) of glycerol/water mixture (C₃H₈O₃/H₂O, 10% w/w) was investigated putting in evidence the influence of the preparation method; sol–gel in basic medium (SGB) and impregnation on an in-house prepared sol–gel γ-Al₂O₃ support (SGI). All developed catalysts were characterized by ICP-AES, TPR-H₂, in-situ heating XRD-O₂, DSC/TG-N₂/O₂ and ex-situ reduction of XRD-H_2, N₂ physisoption and TEM techniques. The results indicate that SGI method and calcination treatment at 750 °C were crucial in extending the catalytic useful life of NiPt-containing γ-Al₂O₃ catalysts, resulting in an adequate distribution of NiPt metallic particles and good stability of γ-Al₂O₃ support against the severe hydrothermal conditions of APR process. The SGI method led to form stable NiPt catalysts with relatively big Ni particles and stable hydrothermal properties of γ-Al₂O₃ support, while the SGB catalysts exhibited well-dispersed Ni particles but unstable catalytic behavior. These last catalysts presented high glycerol conversions during the first hours of APR glycerol/water reaction, however, an important decrease in terms of glycerol conversion was observed after 24 h time-on-stream. The experimental results suggested that the most suitable stable and active catalyst was the NiPt/ASGI7 (better than >NiPt/ASGI6 > NiPt/ASGI5 >>> NiPt/ASGB7). This catalyst showed best catalytic activity and good catalytic stability along 56 h of time-on-stream, reaching, at steady state, highest total glycerol conversion (≈79%) and glycerol into gaseous products (≈57%) in APR reaction of glycerol/water mixture for hydrogen generation.     

Enhancing hydrogen production by dry reforming process with strontium promoter

Hydrogen is an ideal energy carrier and can play a very important role in the energy system. The present study investigated the enhancement of hydrogen production from catalytic dry reforming process. Two catalysts namely Ni/γ-Al₂O₃ and Co/γ-Al₂O₃ promoted with different amounts of strontium were used to explore selectivity and yield of hydrogen production. Spent and fresh catalysts were characterized using techniques such as BET, XRD, H₂-TPR, CO₂-TPD, TGA and O₂-TPO. The catalyst activity and characterization results displayed stability improvement due to addition of Sr promoter. The least coke formations i.e. 3.8 wt% and 5.1 wt% were obtained using 0.75 wt% Sr doped in Ni/γ-Al₂O₃ and 0.5 wt% Sr doped in Co/γ-Al₂O₃ catalysts respectively. Time on stream tests of promoted catalysts for about six hours at 700 °C showed stable hydrogen selectivity. Moreover, the hydrogen selectivity was significantly improved by the addition of Sr in Ni and Co based catalysts. For instance the hydrogen selectivity increased from 45.9% to 47.8% for Ni/γ-Al₂O₃ and from 48% to 50.9% for Co/γ-Al₂O₃ catalyst by the addition of 0.75 wt% Sr in Ni/γ-Al₂O₃ and 0.5 wt% Sr in Co/γ-Al₂O₃ catalyst respectively.     

Catalytic performances of Ni-based catalysts on supercritical water gasification of phenol solution and coal-gasification wastewater

Activity and stability of the supported Ni-based catalysts for the gasification performances of phenol solution and coal-gasification wastewater in supercritical water were studied in a continuous reactor at 480 °C, 25 MPa and oxygen ratio of 0.2 for 50 h operation. The influences of the supports (γ-Al₂O₃, active carbon (AC) and carbon nanotube (CNT)) on gas yields, gasification efficiencies for phenol solution were investigated, and the loading amount of Ni were optimized. Results showed that the catalytic activity and the stability of the catalysts followed the order of Ni/CNT > Ni/AC > Ni/γ-Al₂O₃. The activity of Ni/AC and Ni/γ-Al₂O₃ decreased after 30 h continuous operation, and there occurred significant leaching of Ni²⁺. For Ni/CNT catalyst, H₂ yield increased obviously when the loading amount of Ni lower than 15 wt%, while increased little at higher loading amount. Then, 15 wt% Ni/CNT with a thickness of 1.5 mm was coated on 316 L stainless steel (SS316L, an economic material usually used as the reactor material), which can act as a "catalytic tube wall" in reactor. The catalytic activity and corrosion resistance of Ni/CNT/SS316L for the gasification of real coal-gasification wastewater were studied. Results showed that Ni/CNT/SS316L gave a great positive effect on H₂ production. H₂ yield increased from 25.36 mmol/g (total organic carbon) without catalyst to 75.12 mmol/g (total organic carbon) with Ni/CNT/SS316L after operated for 20 h, respectively. However, obvious pealing of the coating was found after 50 h operation. Further study is necessary for the improvement of the coating preparation method.     

Catalytic characteristics of innovative Ni/slag catalysts for syngas production and tar removal from biomass pyrolysis

In this study, innovative Ni-based catalysts supported by five typical slag carriers (magnesium slag (MS), steel slag (SS), blast furnace slag (BFS), pyrite cinder (PyC) and calcium silicate slag (CSS)) were prepared by wet impregnation. With the prepared catalysts and Ni/γ-Al₂O₃ catalyst, catalytic reforming of pyrolysis volatiles from pine sawdust for syngas production and tar removal was investigated. The catalysts were characterized by BET, XRD, SEM, TEM and Raman. The catalytic performances of the six catalysts were decreasing in the following order: Ni/MS > Ni/γ-Al₂O₃ > Ni/SS > Ni/BFS > Ni/CSS > Ni/PyC. Ni/MS catalyst exhibited excellent catalytic reactivity as well as thermal stability in terms of tar conversion (95.19%), gas yield (1.46 Nm³/kg) and CO₂ capture ability (CO₂ yield of 0.5%). Both amorphous carbon and graphite-type carbon were formed on the catalysts after catalytic reforming and the D/G ratio (the relative intensity ratio of the D-band to the G-band) was positively correlated to the catalytic activity.     

Catalytic reforming of glycerol in supercritical water with nickel-based catalysts

The catalytic performance of nickel catalysts supported on La₂O₃, α-Al₂O₃, γ-Al₂O₃, ZrO₂, and YSZ for supercritical water reforming of glycerol was investigated. Experiments were conducted in a tubular reactor made of Inconel-625 with the temperature range of 723–848 K under a pressure of 25 MPa. Carbon formation causing operation failure was observed for α-Al₂O₃, γ-Al₂O₃ and ZrO₂ at temperatures higher than 748, 798 and 823 K, respectively. Ni/La₂O₃ exhibited the highest H₂ yield where almost complete conversion was obtained at 798 K. Moderate space velocities (WHSV = 6.45 h⁻¹) and glycerol feed concentration (5wt.%) favor high hydrogen selectivity and yield. Methanation is favored at a low WHSV or high glycerol feed concentration, resulting in a lower H₂ yield. Increasing Ni loading on the Ni/La₂O₃ catalyst strongly promoted the reforming, water–gas shift, and methanation reactions, which contributed significantly to the product species distribution.     

Steam reforming of dimethyl ether over Cu–Ni/γ-Al2O3 bi-functional catalyst prepared by deposition–precipitation method

Cu–Ni/γ-Al₂O₃ catalysts with different metal contents for dimethyl ether steam reforming (DME SR) were prepared by the method of deposition–precipitation. Characterization of specific surface area measurement (BET), X-ray diffraction (XRD) and hydrogen temperature-programmed reduction (H₂-TPR) revealed that nickel improved the dispersion of copper, increased the interaction between copper and γ-Al₂O₃, and therefore, inhibited the sintering of copper. Ammonia temperature-programmed desorption (NH₃-TPD) showed that metal particles could occupy the acid sites, leading to the decrease in acid amount and acid strength of Cu–Ni/γ-Al₂O₃ catalyst. Kinetic measurements indicated that γ-Al₂O₃ is vital for DME SR and a higher content of γ-Al₂O₃ in catalyst was needed. The addition of nickel suppressed the water gas shift (WGS) reaction. Initial durability testing showed that the conversion of DME over Cu–Ni/γ-Al₂O₃ catalyst was always almost complete during the 30 h experimental reaction time. Therefore, Cu–Ni/γ-Al₂O₃ could be a potential DME SR catalyst for the production of hydrogen.     

CO2 reforming of methane on Ni/γ-Al2O3 catalyst prepared by dielectric barrier discharge hydrogen plasma

Ni/γ-Al₂O₃ catalyst was prepared by direct treatment of Ni(NO₃)₂/γ-Al₂O₃ precursor with dielectric barrier discharge (DBD) hydrogen plasma at different input powers, characterized by XRD, H₂-TPR, CO₂-TPD, N₂ adsorption and TEM, respectively, and used as the catalyst for CO₂ reforming of methane (CRM). The results showed that the input power obviously affected the reduction degree and catalytic performances of catalysts. Low input power under 40 W mainly resulted in the decomposition of nickel nitrate into Ni oxides. The reduction degree, catalytic activity and stability increase with the input power. Similar catalytic performances in CRM reaction can be obtained when the power exceeds 80 W. Compared with the Ni/Al₂O₃ catalyst prepared by traditional method, Ni/γ-Al₂O₃ samples prepared by H₂ DBD plasma exhibit better activities, stability and anti-carbon deposit performances. It is mainly ascribed to smaller Ni particle size, more basic sites and weaker basicity. The increase of Ni particle sizes due to the sintering at high temperature results in the decrease of catalytic activities and coke formation.     

Enhanced selectivity of syngas in partial oxidation of methane: A new route for promising Ni-alumina catalysts derived from Ni/γ-AlOOH with modified Ni dispersion

Partial oxidation of methane was studied over new Ni nanocatalysts prepared from Ni-impregnated γ-AlOOH, which were compared with their counterparts derived from impregnated γ-Al₂O₃ and α-Al₂O₃. The prepared catalysts were characterized by powder X-ray diffraction (XRD), N₂-sorption, H₂-temperatue programmed reduction, scanning electron microscopy, transmission electron microscopy, thermal gravimetric analysis, CO₂- and NH₃-temperature-programmed desorption, Raman spectroscopy, CO chemisorption, and diffuse reflectance infrared Fourier transform spectroscopy of adsorbed CO. Employing γ-AlOOH as the support precursor resulted in significantly improved textural properties and catalytic activity. The structure of the support precursor and its surface properties showed a strong influence on the type of Ni active species and their interactions with the support. γ-AlOOH-derived catalysts showed NiO as the dominant Ni species when calcined at 500°C to 650°C, while NiAl₂O₄ became the sole phase at higher temperatures. On the other hand, mixtures of NiO and NiAl₂O₄ formed over γ-Al₂O₃, calcined before impregnation, regardless of the precalcination temperature. All γ-AlOOH-derived catalysts showed higher specific surface areas compared to their counterparts derived from impregnated γ-Al₂O₃. Upon calcination at moderate temperatures, γ-AlOOH-derived catalysts also showed modified textural and morphological properties of the Ni active particles, including higher Ni dispersion, larger metal surface area, and smaller Ni crystallites. The support precursor and the pretreatment conditions showed a strong influence on the catalytic performance, which was referred to their significant effect on the type of the Ni species and interactions with the support. All catalysts showed higher catalytic activity than the α-Al₂O₃-derived catalyst, with CH₄ conversion between 86% and 88.5% at 700°C. While γ-AlOOH- and γ-Al₂O₃-derived catalysts calcined at 650°C showed a stable CH₄ conversion around 88%, and higher syngas selectivity than the other catalysts, Ni/γ-AlOOH-650 showed the highest selectivity to syngas, with a H₂/CO ratio very close to 2.0. The improved Ni dispersion and the enhanced syngas selectivity obtained in the preset work demonstrate that using γ-AlOOH as a support precursor holds a great promise for the development of a new route for more efficient Ni catalysts compared with the widely studied γ-Al₂O₃ and α-Al₂O₃ support precursors.     

Hydrogen production by steam reforming of liquefied natural gas (LNG) over Ni/Al2O3–ZrO2 xerogel catalysts: Effect of calcination temperature of Al2O3–ZrO2 xerogel supports

Al₂O₃–ZrO₂ (AZ) xerogel supports prepared by a sol-gel method were calcined at various temperatures. Ni/Al₂O₃–ZrO₂ (Ni/AZ) catalysts were then prepared by an impregnation method for use in hydrogen production by steam reforming of liquefied natural gas (LNG). The effect of calcination temperature of AZ supports on the catalytic performance of Ni/AZ catalysts in the steam reforming of LNG was investigated. Crystalline phase of AZ supports was transformed in the sequence of amorphous γ-Al₂O₃ and amorphous ZrO₂ → θ-Al₂O₃ and tetragonal ZrO₂ → (θ + α)-Al₂O₃ and (tetragonal + monoclinic) ZrO₂ → α-Al₂O₃ and (tetragonal + monoclinic) ZrO₂ with increasing calcination temperature from 700 to 1300 °C. Nickel oxide species were strongly bound to γ-Al₂O₃ and θ-Al₂O₃ in the Ni/AZ catalysts through the formation of solid solution. In the steam reforming of LNG, both LNG conversion and hydrogen composition in dry gas showed volcano-shaped curves with respect to calcination temperature of AZ supports. Nickel surface area of Ni/AZ catalysts was well correlated with catalytic performance of the catalysts. Among the catalysts tested, Ni/AZ1000 (nickel catalyst supported on AZ support that had been calcined at 1000 °C) with the highest nickel surface area showed the best catalytic performance. Well-developed and pure tetragonal phase of ZrO₂ in the AZ1000 support played an important role in the adsorption of steam and the subsequent spillover of steam from the support to the active nickel.