Surface Nickel Aluminate Research Articles

From ethene to propene (ETP) on tailored silica-alumina supports with isolated Ni(ii) sites: uncovering the importance of surface nickel aluminate sites and the carbon-pool mechanism.

Catalysts with well-defined isolated Ni(ii) surface sites have been prepared on three silica-based supports. The outer shells of the support were comprised either of an amorphous aluminosilicate or amorphous alumina (AlO x ) layer - associated with a high and low density of strong Brønsted acid sites (BAS), respectively. When tested for ethene-to-propene conversion, Ni catalysts with a higher density of strong BAS demonstrate a higher initial activity and productivity to propene. On all three catalysts, the propene productivity correlates closely with the concentration of C8 aromatics, suggesting that propene may form via a carbon-pool mechanism. While all three catalysts deactivate with time on stream, the deactivation of catalysts with Ni(ii) sites on AlO x , i.e., containing surface Ni aluminate sites, is shown to be reversible by calcination (coke removal), in contrast to the deactivation of surface Ni silicate or aluminosilicate sites, which deactivate irreversibly by forming Ni nanoparticles.

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.

Hydrogen production by steam reforming of liquefied natural gas (LNG) over mesoporous alkaline earth metal-promoted nickel-alumina xerogel catalysts

A series of mesoporous alkaline earth metal-promoted nickel-alumina xerogel (M/NA, M=Mg, Ca, Sr, and Ba) catalysts were prepared by a single-step epoxide-driven sol–gel method and a subsequent incipient wetness impregnation method. They were applied to the hydrogen production by steam reforming of liquefied natural gas (LNG). For reference, a nickel-alumina xerogel catalyst without promoter (NA) was prepared by a single-step epoxide-driven sol–gel method. The catalysts were characterized by N2 adsorption–desorption, ICP-AES, XRD, TPR, H2-chemisorption, TEM, and CHNS analyses. Surface area and pore volume of M/NA catalysts were smaller than those of NA catalyst due to blockage of mesopores by promoters during the impregnation step. Both NA and M/NA catalysts exhibited X-ray diffraction patterns corresponding to nickel aluminate phase. In the TPR measurements, it was revealed that all the catalysts retained surface nickel aluminate phase, regardless of the identity of alkaline earth metal. Nickel surface area of reduced catalysts decreased in the order of Mg/NA>Sr/NA>Ca/NA>NA>Ba/NA. In the hydrogen production by steam reforming of LNG, the catalytic performance of NA and M/NA catalysts was well correlated with the nickel surface area of the catalysts; LNG conversion and hydrogen yield increased with increasing nickel surface area. Among the catalysts tested, Mg/NA catalyst with the highest nickel surface area showed the best catalytic performance. The amount of carbon deposition on the used M/NA catalysts was less than that on the used NA catalyst.

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

A trimethylbenzene (TMB)-assisted ordered mesoporous nickel–alumina catalyst (denoted as TNA) was prepared by a single-step evaporation-induced self-assembly (EISA) method, and it was applied to the hydrogen production by steam reforming of liquefied natural gas (LNG). For comparison, an ordered mesoporous nickel–alumina catalyst (denoted as NA) was also prepared by a single-step EISA method in the absence of TMB. Pore volume and average pore diameter of TNA catalyst were larger than those of NA catalyst due to structural modification caused by TMB addition in the preparation of TNA catalyst. In addition, TNA catalyst showed less ordered mesoporous array than NA catalyst. Both NA and TNA catalysts exhibited diffraction patterns corresponding to nickel aluminate phase, and they retained surface nickel aluminate phase with high stability and reducibility. Crystallite size of metallic nickel in the reduced TNA catalyst was smaller than that in the reduced NA catalyst due to strong nickel–alumina interaction of surface nickel aluminate phase over TNA catalyst. In the hydrogen production by steam reforming of LNG, TNA catalyst with small crystallite size of metallic nickel showed a better catalytic performance than NA catalyst in terms of LNG conversion and hydrogen yield. Furthermore, steam reforming reaction rather than water–gas shift reaction favorably occurred over TNA catalyst.

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 Ni/Al atomic ratio of mesoporous Ni–Al 2O 3 aerogel catalysts on their catalytic activity for hydrogen production by steam reforming of liquefied natural gas (LNG)

Mesoporous Ni–Al 2O 3 ( XNiAE) aerogel catalysts with different Ni/Al atomic ratio ( X) were prepared by a single-step sol-gel method and a subsequent CO 2 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.

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 CO 2 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.

Mesoporous Nickel–Alumina Catalysts for Hydrogen Production by Steam Reforming of Liquefied Natural Gas (LNG)

Recent progress on the mesoporous nickel–alumina catalysts for hydrogen production by steam reforming of liquefied natural gas (LNG) was reported in this review. A number of mesoporous nickel–alumina composite catalysts were prepared by a single-step surfactant-templating method using cationic, anionic, and non-ionic surfactant as structure-directing agents for use in hydrogen production by steam reforming of LNG. For comparison, nickel catalysts supported on mesoporous aluminas were also prepared by an impregnation method. The effect of preparation method and surfactant identity on physicochemical properties and catalytic activities of mesoporous nickel–alumina catalysts in the steam reforming of LNG was investigated. Regardless of preparation method and surfactant identity, nickel oxide species were finely dispersed on the surface of mesoporous nickel–alumina catalysts through the formation of surface nickel aluminate phase. However, nickel dispersion and nickel surface area of mesoporous nickel–alumina catalysts were strongly affected by the preparation method and surfactant identity. It was found that nickel surface area of mesoporous nickel–alumina catalyst served as one of the important factors determining the catalytic performance in hydrogen production by steam reforming of LNG. Among the catalysts tested, a mesoporous nickel–alumina composite catalyst prepared by a single-step non-ionic surfactant-templating method exhibited the best catalytic performance due to its highest nickel surface area.

Hydrogen Production by Steam Reforming of Liquefied Natural Gas Over Mesoporous Ni-Al2O3 Composite Catalyst Prepared by a Single-step Non-ionic Surfactant-templating Method

A mesoporous Ni-Al2O3 composite catalyst (Ni-A-NS) was prepared by a single-step non-ionic surfactant-templating method for use in hydrogen production by steam reforming of liquefied natural gas (LNG). For comparison, a nickel catalyst supported on mesoporous alumina (Ni/A-NS) was also prepared by an impregnation method. The effect of physicochemical properties on the performance of Ni-A-NS catalyst in the steam reforming of LNG was investigated. Ni-A-NS catalyst retained superior textural properties compared to Ni/A-NS catalyst. Nickel oxide species were highly dispersed on the surface of both Ni/A-NS and Ni-A-NS catalysts through the formation of surface nickel aluminate phase. Although both Ni/A-NS and Ni-A-NS catalysts exhibited a stable catalytic performance, Ni-A-NS catalyst showed a better catalytic performance than Ni/A-NS catalyst in the steam reforming of LNG. High nickel surface area and high nickel dispersion of Ni-A-NS catalyst played an important role in enhancing the dehydrogenation reaction of hydrocarbon species and the gasification reaction of adsorbed carbon species in the steam reforming of LNG. High reducibility of Ni-A-NS catalyst was also responsible for its high catalytic performance.

Hydrogen production by steam reforming of liquefied natural gas (LNG) over Ni–Al 2O 3 catalysts prepared by a sequential precipitation method: Effect of precipitation agent

Mesoporous Ni–Al 2O 3 catalysts (denoted as NiAl–NH 4OH, NiAl–KOH, NiAl–NaOH, and NiAl–Na 2CO 3) were prepared by a sequential precipitation method using various basic solutions (NH 4OH, KOH, NaOH, and Na 2CO 3) as precipitation agents. They were then applied to the hydrogen production by steam reforming of liquefied natural gas (LNG). The effect of precipitation agent on the physicochemical properties and catalytic activities of mesoporous Ni–Al 2O 3 catalysts in the steam reforming of LNG was investigated. Physicochemical properties of Ni–Al 2O 3 catalysts were strongly influenced by the precipitation agent. Surface area and pore volume of Ni–Al 2O 3 catalysts decreased in the order of NiAl–NH 4OH > NiAl–KOH > NiAl–NaOH > NiAl–Na 2CO 3. Regardless of the identity of precipitation agent, nickel species were finely dispersed on the surface of Ni–Al 2O 3 catalysts through the formation of surface nickel aluminate phase. LNG conversion and hydrogen composition in dry gas decreased in the order of NiAl–NH 4OH > NiAl–KOH > NiAl–NaOH > NiAl–Na 2CO 3. Nickel surface area played an important role in determining the catalytic performance of Ni–Al 2O 3 catalysts. Among the catalysts tested, NiAl–NH 4OH catalyst with the highest nickel surface area showed 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)

Abstract Mesoporous Ni–Al 2 O 3 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–Al 2 O 3 catalysts on their catalytic activity for steam reforming of LNG was investigated. Physicochemical properties of Ni–Al 2 O 3 catalysts were strongly influenced by the preparation method of Ni–Al 2 O 3 catalysts. Surface area, pore volume, and average pore size of Ni–Al 2 O 3 catalysts decreased in the order of NiAl-SP > NiAl-CP > NiAl-IP. Nickel species strongly interacted with Al 2 O 3 supports through the formation of nickel aluminate phase. Surface nickel aluminate phase of Ni–Al 2 O 3 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–Al 2 O 3 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.

From Al 2O 3-supported Ni(II)–ethylenediamine complexes to CO hydrogenation catalysts: Characterization of the surface sites and catalytic properties

Ni (15 wt%)/Al 2O 3 catalysts prepared by decomposition of supported Ni(II)–ethylenediamine complexes in inert atmosphere, followed by post-treatment in hydrogen, are able to catalyze carbon monoxide hydrogenation at temperatures lower than for a catalyst prepared from nickel nitrate and containing a fraction of surface nickel aluminate. Unlike the latter, the catalyst prepared from Ni(II)–en complexes exhibits mostly surface metallic sites and is more stable under reaction despite the absence of nickel aluminate. Deactivation occurs during the reaction, probably by carbon deposition, but less strongly than for an ex-nickel nitrate catalyst.

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.

Hydrogen production by steam reforming of liquefied natural gas over a nickel catalyst supported on mesoporous alumina xerogel

Mesoporous alumina xerogel (A-SG) is prepared by a sol–gel method for use as a support for a nickel catalyst. The Ni/A-SG catalyst is then prepared by an impregnation method, and is applied to hydrogen production by steam reforming of liquefied natural gas (LNG). The effect of the mesoporous alumina xerogel support on the catalytic performance of Ni/A-SG catalyst is investigated. For the purpose of comparison, a nickel catalyst supported on commercial alumina (A-C) is also prepared by an impregnation method (Ni/A-C). Both the hydroxyl-rich surface and the electron-deficient sites of the A-SG support enhance the dispersion of the nickel species on the support during the calcination step. The formation of the surface nickel aluminate phase in the Ni/A-SG catalyst remarkably increases the reducibility and stability of the catalyst. Furthermore, the high-surface area and the well-developed mesoporosity of the Ni/A-SG catalyst enhance the gasification of surface hydrocarbons that are adsorbed in the reaction. In the steam reforming of LNG, the Ni/A-SG catalyst exhibits a better catalytic performance than the Ni/A-C catalyst in terms of LNG conversion and hydrogen production. Moreover, the Ni/A-SG catalyst shows strong resistance toward catalyst deactivation.

Methanation sites on a low loading Ni/Al 2O 3 catalyst

A low loading Ni/Al 2O 3 catalyst (0.74 wt.-% Ni) is shown to exhibit reaction processes that are similar to those on higher loading nickel catalysts during temperature-programmed reaction (TPR) in which adsorbed carbon monoxide is hydrogenated. That is, carbon monoxide adsorbs on reduced nickel and transfers to the Al 2O 3 support to form an H-CO complex, which is probably a methoxy species. The methoxy is hydrogenated at a slower rate than carbon monoxide adsorbed on nickel. However, because only 3% of the nickel is on the surface as reduced nickel, the Al 2O 3 surface area is much larger than the nickel surface area and most of the carbon monoxide adsorbed on nickel at 300 K transfers to the Al 2O 3 surface during TPR. Also, an additional methanation site of intermediate activity was observed on the 0.74% Ni/Al 2O 3 catalyst. By comparison to TPR on oxidized 0.74% Ni/Al 2O 3 and bulk NiAl 2O 4, both oxidized and reduced, the third site is assigned to carbon monoxide adsorbed on unreduced nickel on the surface: either surface nickel aluminate or nickel oxide. The surface of bulk NiAl 2O 4 is also shown to be reduced at 775 K in hydrogen to form Al 2O 3 and reduced nickel. Variations in heating rate, adsorption temperature, and hydrogen pressure during TPR are used to identify the distinct reaction sites; these variations also demonstrate the ability of TPR to detect adsorption on sites present in low concentrations.

Evidence for the participation of surface nickel aluminate sites in the steam reforming of methane over nickel/alumina catalysts

The specific activities of various Ni Al 2O 3 catalysts for the reaction of CH 4 with H 2O have been obtained and have been shown to vary markedly with catalyst preparation and to differ considerably from the specific activities of pure nickel. This has been explained by suggesting that the unreduced catalysts contain surface nickel aluminate phases which, on reduction, give monodispersed nickel atoms closely associated with alumina sites in addition to metallic crystallites arising from the reduction of nickel oxide. The results of exchange experiments using deuterium and H 2 18O are presented in support of the suggestion that the monodispersed nickel atoms probably participate in the CH 4 + H 2O reaction.