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.     

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.     

Hydrogen production by steam reforming of liquefied natural gas (LNG) over mesoporous nickel–alumina aerogel catalyst

A mesoporous nickel–alumina aerogel catalyst (NiAE-SS) was prepared by a single-step sol–gel method and a subsequent CO₂ supercritical drying method for use in hydrogen production by steam reforming of liquefied natural gas (LNG). For comparison, a nickel catalyst supported on alumina aerogel (Ni/AE-IP) was also prepared by an impregnation method. The effect of preparation method of supported nickel catalysts on their physicochemical properties and catalytic performance in the steam reforming of LNG was investigated. NiAE-SS catalyst retained superior textural properties compared to Ni/AE-IP catalyst. Nickel species were finely dispersed on the surface of both Ni/AE-IP and NiAE-SS catalysts through the formation of surface nickel aluminate phase. Although both Ni/AE-IP and NiAE-SS catalysts exhibited a stable catalytic performance, NiAE-SS catalyst showed a better catalytic performance than Ni/AE-IP catalyst in terms of LNG conversion and hydrogen yield. High nickel surface area, high nickel dispersion, and well-developed mesoporosity of NiAE-SS catalyst played an important role in enhancing the catalytic performance in the steam reforming of LNG. Uniformly distributed metallic nickel particles in the NiAE-SS catalyst were also responsible for its high catalytic performance.     

Effect of Ni/Al atomic ratio of mesoporous Ni–Al2O3 aerogel catalysts on their catalytic activity for hydrogen production by steam reforming of liquefied natural gas (LNG)

Mesoporous Ni–Al₂O₃ (XNiAE) aerogel catalysts with different Ni/Al atomic ratio (X) were prepared by a single-step sol-gel method and a subsequent CO₂ supercritical drying method. The effect of Ni/Al atomic ratio of mesoporous XNiAE aerogel catalysts on their physicochemical properties and catalytic activity for steam reforming of liquefied natural gas (LNG) was investigated. Textural properties and chemical properties of XNiAE catalysts were strongly influenced by Ni/Al atomic ratio. Nickel species were highly dispersed on the surface of XNiAE catalysts through the formation of surface nickel aluminate phase. In the steam reforming of LNG, both LNG conversion and hydrogen yield showed volcano-shaped curves with respect to Ni/Al atomic ratio. Average nickel diameter of XNiAl catalysts was well correlated with LNG conversion and hydrogen yield over the catalysts. Among the catalysts tested, 0.35NiAE (Ni/Al = 0.35) catalyst with the smallest average nickel diameter showed the best catalytic performance. The highest surface area, the largest pore volume, the largest average pore size, and the highest reducibility of 0.35NiAE catalyst were also partly responsible for its superior catalytic performance.     

Effect of calcination temperature of mesoporous alumina xerogel (AX) supports on hydrogen production by steam reforming of liquefied natural gas (LNG) over Ni/AX catalysts

Mesoporous alumina xerogel (AX) supports prepared by a sol–gel method were calcined at various temperatures. Ni/mesoporous alumina xerogel (Ni/AX) catalysts were then prepared by an impregnation method, and were applied to the hydrogen production by steam reforming of liquefied natural gas (LNG). The effect of calcination temperature of AX supports on the catalytic performance of Ni/AX catalysts in the steam reforming of LNG was investigated. Physical and chemical properties of AX supports and Ni/AX catalysts were strongly influenced by the calcination temperature of AX supports. Crystalline structure of AX supports was transformed in the sequence of γ-alumina → (γ + θ)-alumina → θ-alumina → (θ + α)-alumina with increasing calcination temperature from 700 to 1000 °C. Nickel species were strongly bonded to the divalent vacancy of γ-alumina, (γ + θ)-alumina, and θ-alumina through the formation of nickel aluminate phase. 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 AX supports. Among the catalysts tested, Ni/AX-900 (nickel catalyst supported on AX that had been calcined at 900 °C) showed the best catalytic performance. The smallest nickel crystalline size and the strongest nickel–alumina interaction were responsible for high catalytic performance of Ni/AX-900 catalyst in the steam reforming of LNG.     

Hydrogen production by steam reforming of liquefied natural gas (LNG) over mesoporous Ni-Al2O3 aerogel catalyst prepared by a single-step epoxide-driven sol-gel method

A mesoporous Ni-Al₂O₃ aerogel catalyst was prepared by a single-step epoxide-driven sol-gel method and a subsequent supercritical CO₂ drying method (NA-ES catalyst). For comparison, a mesoporous Ni-Al₂O₃ aerogel catalyst was also prepared by a single-step alkoxide-based sol-gel method and a subsequent supercritical CO₂ drying method (NA-AS catalyst). Differences in physicochemical properties and catalytic activities of mesoporous Ni-Al₂O₃ aerogel catalysts in the steam reforming of liquefied natural gas (LNG) were investigated. Textural properties of Ni-Al₂O₃ aerogel catalysts were affected by the preparation method. Nickel species were highly dispersed in alumina through the formation of nickel aluminate phase in both NA-ES and NA-AS catalysts. However, chemical states of Al atoms in both catalysts were quite different. In addition, nickel species in the NA-ES catalyst exhibited high reducibility and high dispersion compared to those in the NA-AS catalyst. In the steam reforming of LNG, NA-ES catalyst exhibited a better catalytic performance than NA-AS catalyst in terms of LNG conversion and hydrogen yield, although both catalysts showed a stable catalytic performance during the reaction without deactivation behavior. Furthermore, NA-ES catalyst with small average nickel diameter suppressed water-gas shift reaction. Reducibility and dispersion of nickel species served as important factors determining the catalytic performance of the catalysts.     

Hydrogen production by steam reforming of liquefied natural gas (LNG) over ordered mesoporous nickel–alumina catalyst

An ordered mesoporous nickel–alumina catalyst (denoted as OMNA) was prepared by a single-step evaporation-induced self-assembly method, and it was applied to the hydrogen production by steam reforming of liquefied natural gas (LNG). For comparison, a nickel catalyst supported on ordered mesoporous alumina support (denoted as Ni/OMA) was also prepared by an impregnation method. Although both Ni/OMA and OMNA catalysts retained unidimensionally ordered mesoporous structure, textural properties of the catalysts were significantly affected by the preparation method. Nickel species were finely dispersed in the OMNA catalyst as a form of surface nickel aluminate with a high degree of nickel-saturation. On the other hand, both bulk nickel oxide and surface nickel aluminate phases were formed in the network of Ni/OMA catalyst. Nickel species in the OMNA catalyst exhibited not only high reducibility but also strong resistance toward sintering during the reduction process, compared to those in the Ni/OMA catalyst. Both Ni/OMA and OMNA catalysts showed a stable catalytic performance without catalyst deactivation during the steam reforming of LNG due to the confinement effect derived from well-developed ordered mesoporous structure in the catalysts. However, OMNA catalyst with small crystallite size of metallic nickel exhibited higher LNG conversion and hydrogen yield than Ni/OMA catalyst. Furthermore, OMNA catalyst was more active in the steam reforming of LNG than non-ordered mesoporous nickel–alumina catalysts prepared by common surfactant-templating methods using cationic, anionic, and non-ionic surfactants.     

Effect of N2O-mediated calcination on nickel species and the catalytic activity of nickel catalysts supported on γ-Al2O3 in the steam reforming of glycerol

The steam reforming of glycerol over supported nickel catalysts is a promising and cost-effective method for producing hydrogen. The activity of nickel catalysts supported on γ-Al₂O₃ is low, primarily due to the formation of inactive nickel species during high temperature calcination in air. In order to address this problem, a Ni/γ-Al₂O₃ catalyst was prepared by calcination at 700 °C in a nitrous oxide (N₂O) environment. The N₂O calcined catalyst showed an enhanced activity for the steam reforming of glycerol. A variety of characterization techniques (XRD, TPR, XPS and H₂ Chemisorption) confirmed that the high temperature N₂O calcination resulted in a significant decrease in the levels of nickel aluminate. The N₂O calcination also led to an enhancement in the amount of NiO as well as nickel ions present on the surface of the catalyst. Interestingly, compared to an air calcined catalyst, the N₂O calcined catalyst contained larger nickel particles after reduction but the N₂O calcined catalyst had a much larger nickel surface area and dispersion, which resulted in higher glycerol conversion and hydrogen yield.     

Hydrogen production by steam reforming of liquefied natural gas (LNG) over mesoporous Ni-La-Al2O3 aerogel catalysts: Effect of La content

Mesoporous Ni-La-Al₂O₃ aerogel catalysts (denoted as (40-x)NixLa) with different lanthanum content (x) were prepared by a single-step sol-gel method and a subsequent CO₂ supercritical drying method. The effect of lanthanum content on the physicochemical properties and catalytic performance of mesoporous (40-x)NixLa catalysts in the steam reforming of liquefied natural gas (LNG) was investigated. Physicochemical properties of (40-x)NixLa catalysts were strongly influenced by lanthanum content. Dispersion and reducibility of nickel aluminate phase in the (40-x)NixLa catalysts increased with increasing lanthanum content. Small amount of lanthanum addition was effective for dispersion of metallic nickel in the (40-x)NixLa catalysts, but large amount of lanthanum addition was not favorable for nickel dispersion due to the blocking of active sites. In the steam reforming of LNG, both LNG conversion and hydrogen yield showed volcano-shaped curves with respect to lanthanum content. Average nickel diameter of (40-x)NixLa catalysts was well correlated with LNG conversion and hydrogen yield over the catalysts. Among the catalysts tested, 36Ni4La (36 wt% Ni and 4 wt% La) catalyst with the smallest average nickel diameter exhibited the best catalytic performance and the strongest resistance toward carbon deposition in the steam reforming of LNG.     

Effect of preparation method of mesoporous Ni–Al2O3 catalysts on their catalytic activity for hydrogen production by steam reforming of liquefied natural gas (LNG)

Mesoporous Ni–Al₂O₃ catalysts were prepared by impregnation method (NiAl-IP), co-precipitation method (NiAl-CP), and sequential precipitation method (NiAl-SP) for use in hydrogen production by steam reforming of liquefied natural gas (LNG). The effect of preparation method of mesoporous Ni–Al₂O₃ catalysts on their catalytic activity for steam reforming of LNG was investigated. Physicochemical properties of Ni–Al₂O₃ catalysts were strongly influenced by the preparation method of Ni–Al₂O₃ catalysts. Surface area, pore volume, and average pore size of Ni–Al₂O₃ catalysts decreased in the order of NiAl-SP > NiAl-CP > NiAl-IP. Nickel species strongly interacted with Al₂O₃ supports through the formation of nickel aluminate phase. Surface nickel aluminate phase of Ni–Al₂O₃ catalysts was readily reduced after the reduction process, while bulk nickel aluminate phase of NiAl-CP catalyst was hardly reducible. Nickel dispersion and nickel surface area of Ni–Al₂O₃ catalysts decreased in the order of NiAl-SP > NiAl-CP > NiAl-IP. Among the catalysts tested, NiAl-SP catalyst with the highest nickel surface area showed the best catalytic performance in the steam reforming of LNG. Furthermore, finely dispersed nickel species in the NiAl-SP catalyst efficiently suppressed the carbon deposition during the reaction.     

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.     

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.     

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 steam reforming of biomass-derived acetic acid over modified Ni/γ-Al2O3 for sustainable hydrogen production

In order to obtain sustainable H₂, the catalytic steam reforming of acetic acid derived from biomass was performed by using the catalysts modified with basic promoters (Mg, La, Cu, and K). La and K increased the total basicity of Ni/γ-Al₂O₃ by 30.6% and 93.4%, respectively, which could induce ketonization, producing acetone. In contrast, Mg reduced the number of middle and strong basic sites by 17.2% and improved the number of weak basic sites by 5% for Ni/γ-Al₂O₃, which promoted the steam reforming of acetic acid (ca. 100% of H₂ and carbon selectivity at even 450 °C) without ketonization. Moreover, the amount of carbon deposited on Ni/Mg/γ-Al₂O₃ was 55.1% less than that deposited on Ni/γ-Al₂O₃. When Cu was employed, the conversion was ca. 60% with less than 70% of H₂ selectivity, at all temperatures considered herein.     

Hydrogen production by steam reforming of simulated liquefied natural gas (LNG) over mesoporous nickel-M-alumina (M = Ni, Ce, La, Y, Cs, Fe, Co, and Mg) aerogel catalysts

Mesoporous nickel-M-alumina aerogel catalysts (denoted as NiMAE) with different second metal (M = Ni, Ce, La, Y, Cs, Fe, Co, and Mg) were prepared by a single-step sol-gel method and a subsequent CO₂ supercritical drying method. The effect of second metal of mesoporous nickel-M-alumina aerogel catalysts on their physicochemical properties and catalytic activity for steam reforming of simulated liquefied natural gas (LNG) was investigated. Textural and chemical properties of NiMAE catalysts were strongly influenced by the identity of second metal. Nickel species were highly dispersed on the surface of NiMAE catalysts through the formation of nickel aluminate phase. In the steam reforming of LNG, both LNG conversion and hydrogen yield decreased in the order of NiLaAE > NiCeAE > NiYAE > NiCsAE > NiNiAE > NiFeAE > NiCoAE > NiMgAE. Average nickel diameter of NiMAE catalysts was well correlated with LNG conversion and hydrogen yield over the catalysts. Among the catalysts tested, NiLaAE catalyst exhibited the best catalytic performance due to its smallest average nickel diameter. Furthermore, NiLaAE catalyst exhibited a strong capability of facilitating heat and mass transfer of reactant and product during the steam reforming of LNG. Water-gas shift reaction governed the steam reforming reaction over NiLaAE catalyst under the steam-rich reaction condition (steam/carbon > 2).     

Hydrogen production by steam reforming of liquefied natural gas (LNG) over nickel catalyst supported on mesoporous alumina prepared by a non-ionic surfactant-templating method

A mesoporous alumina (A-NS) support was prepared by a non-ionic surfactant-templating method. A nickel catalyst supported on mesoporous alumina (Ni/A-NS) was then prepared by an impregnation method for use in hydrogen production by steam reforming of liquefied natural gas (LNG). For comparison, a nickel catalyst supported on commercial alumina (Ni/A-C) was also prepared by an impregnation method. Well-developed mesoporosity of A-NS support and strong metal-support interaction of Ni/A-NS catalyst greatly enhanced the nickel dispersion and nickel surface area through the formation of surface nickel aluminate. In the steam reforming of LNG, Ni/A-NS catalyst showed a better catalytic performance than Ni/A-C catalyst. High nickel surface area, high nickel dispersion, and well-developed mesoporosity of Ni/A-NS catalyst not only provided a large number of active nickel sites, but also suppressed the carbon deposition and nickel sintering during the reaction. Furthermore, Ni/A-NS catalyst exhibited a better catalytic performance than nickel catalyst supported on mesoporous alumina prepared by either an anionic surfactant-templating method or a cationic surfactant-templating method.     

Promotional effect of Mg in trimetallic nickel-manganese-magnesium nanocrystalline catalysts in CO2 reforming of methane

In the present paper, the dry reforming reaction was studied over the 10 wt%Ni-3wt.%Mn-x wt.% Mg (x = 2, 4 and 6 wt%) catalysts supported on γ-Al₂O₃ with mesoporous structure. The physicochemical characteristics of the samples were determined by XRD, BET, TPO, and SEM techniques. Mesoporous γ-Al₂O₃ carrier with the high BET area (186 m²/g) was synthesized by a simple sol–gel method and the Ni, NiMn and Mg promoted catalysts possessed nanocrystalline mesoporous structure with the BET area in the range of 127–176 m²/g. The average pore radius of the prepared catalysts were smaller than 11 nm. All the synthesized samples exhibited a CH₄ conversion in the range of 60–65% at 700 °C. The small differences in methane conversion in all catalysts could be related to the same nickel loading. According to the TPR results, the Mg addition caused an increase in the reducibility of the nickel catalyst and the Mg-promoted sample exhibited a higher conversion compared to the monometallic catalyst, due to its higher reducibility. The results showed that the textural characteristics of the catalysts were affected by the content of Mg. The results indicated that the NiMn/Al₂O₃ catalyst promoted by 4 wt% Mg showed the highest CH₄ conversion in all studied reaction temperatures (550–700 °C). Furthermore, only one oxidation peak was detected for all catalysts in TPO analysis, which was related to the filamentous form carbon. The 10Ni/Al₂O₃ and 10Ni3Mn4Mg/Al₂O₃ catalysts exhibited the highest and the lowest amount of deposited filamentous carbon, respectively. The 10Ni3Mn4Mg/Al₂O₃ catalyst was stable during the 20 h time on stream without any decline in CH₄ conversion.     

The influence of Ni loading on coke formation in steam reforming of acetic acid

Steam reforming of acetic acid on Ni/γ-Al₂O₃ with different nickel loading for hydrogen production was investigated in a tubular reactor at 600 °C, 1 atm, H2O/HAc = 4, and WHSV = 5.01 g-acetic acid/g-cata.h^?1. The catalysts were characterized by temperature programmed oxidation (TPO) and differential thermal analysis (DTA), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The results showed that the amount of deposited carbidic-like carbon decreased and graphitic-like carbon increased with Ni loading increasing from 9 to 15 wt%. The Ni/γ-Al₂O₃ catalyst with 12 wt% Ni loading had higher catalytic activity and lower coke deposited rate.     

Hydrogen production by steam reforming of liquefied natural gas (LNG) over mesoporous nickel–phosphorus–alumina aerogel catalyst

A mesoporous nickel–phosphorus–alumina aerogel catalyst (NPAA) was prepared by a single-step epoxide-driven sol–gel method and a subsequent supercritical CO₂ drying method for use in the hydrogen production by steam reforming of liquefied natural gas (LNG). In order to investigate the effect of drying method of nickel–phosphorus–alumina catalysts on their physicochemical properties and catalytic activities, a mesoporous nickel–phosphorus–alumina xerogel catalyst (NPAX) was also prepared by a single-step epoxide-driven sol–gel method and a subsequent evaporative drying method for comparison purpose. It was found that supercritical CO₂ drying method was effective for enhancing textural properties of NPAA catalyst. Although both NPAX and NPAA catalysts retained surface nickel aluminate phase, NPAA catalyst showed stronger metal-support interaction than NPAX catalyst. XRD patterns of reduced NPAX and NPAA catalysts revealed that NPAA catalyst retained smaller metallic nickel crystallite than NPAX catalysts. It was also observed that the reduced NPAA catalyst exhibited high nickel dispersion, large amount of strong hydrogen-binding sites, and large amount of methane adsorption compared to the reduced NPAX catalyst. In the steam reforming of LNG, NPAA catalyst with high affinity toward methane showed a better catalytic performance than NPAX catalyst.     

Catalysts evaluation for production of hydrogen gas and carbon nanotubes from the pyrolysis-catalysis of waste tyres

Six different types of catalysts (nickel, iron, and cobalt each supported by γ-Al₂O₃ and activated carbon) that were prepared via impregnation were used to produce hydrogen (H₂) and carbon nanotubes (CNTs) from the pyrolytic product of waste tyres. A two-stage pyrolytic-catalytic reactor was constructed, in which the waste tyre was pyrolyzed in the first pyrolysis reactor, and the resultant pyrolysis vapors underwent the reforming and upgrading step in the downstream catalytic reactor. The results showed that the interaction between the active metal and its support had a remarkable effect on the production of H₂ and CNTs. Compared with the series of γ-Al₂O₃ supported catalysts, all the activated carbon-supported catalysts showed higher H₂ yields and better CNTs quality. For the same catalyst support (γ-Al₂O₃ or activated carbon), the higher yield of H₂ and better quality of CNTs were obtained by the Ni catalysts, followed by the Fe catalysts and the Co catalysts. Among all the catalysts, Ni supported by activated carbon exhibited the best catalytic performance, producing the highest hydrogen yield (59.55 vol.%) and the best CNT quality. Further investigation about the influence of CH₄ and naphthalene as the carbon source on generated CNTs revealed that CH₄ led to longer CNT length and higher graphitization than naphthalene.