Performance Of Ni-based Catalysts Research Articles

Geometrically effective NiAl2O4 formation over macroporous Ni/Al2O3 catalysts and coking resistance in dry reforming of methane

This study aimed to investigate the geometrical effect of macroporosity on the performance of Ni-based catalysts in the dry reforming of methane (DRM). For this, macroporous Ni/Al2O3 catalysts with different Ni contents were synthesized. Characterization experiments on the macroporous Ni/Al2O3 catalysts revealed that the macroporous Al2O3 structure enhanced NiAl2O4 formation by facilitating efficient interactions between the Ni species and accessible Al2O3 sites on the macroporous wall surface during calcination. In a subsequent reduction step, Ni exsolution from the NiAl2O4 structure generated highly dispersed Ni nanoclusters over the macroporous Al2O3. Conversely, non-macroporous Ni/Al2O3 catalysts presented substantial amounts of large isolated Ni nanoparticles at an Ni content of 20 wt%, owing to limited NiAl2O4 formation caused by the lack of accessible Al2O3 sites. The highly dispersed Ni nanoclusters surrounded by oxygen vacancies on the macroporous Ni/Al2O3 catalysts significantly enhanced their catalytic performance in the DRM, evidenced by their high CO2 and CH4 conversions and strong resistance to coking. Moreover, the superior coke resistance ability of the macroporous Ni/Al2O3 catalysts was attributed to the gasification of the coke precursor on Ni nanoclusters surrounded by oxygen vacancies during the DRM.

Performance of Ni-Based Catalysts with La Promoter for the Reforming of Methane in Gasification Process

Performance of Ni-Based Catalysts with La Promoter for the Reforming of Methane in Gasification Process

Synergistic effects of surface acidity and alkalinity of Ni/γ-Al2O3 catalysts in fats and oils hydrodeoxygenation product distribution

The deep utilization of green and renewable chemicals has laid the foundation for sustainable development. Recombining and modifying the long carbon chain structure and oxygen-containing functional groups in fats and oils can prepare important chemical products, such as high-quality second-generation biodiesel and oxygen-containing compounds (fatty alcohols, fatty acids, and esters). To improve the hydrodeoxygenation (HDO) performances of Ni-based catalysts, the effect of surface composition was studied in detail. Acid-base centers of Ni/γ-Al2O3 catalysts were finely regulated by adding metal oxides (ZrO2, CeO2, La2O3, and MgO). It was found that enhancing the basicity of the studied catalyst was conducive to the methyl laurate conversion, but was not conducive to the HDO of oxygen-containing intermediates. In other words, the strong basicity would promote the condensation reaction of oxygen-containing intermediates over Ni-based catalyst. Among the studied catalysts, Ni/La2O3/γ-Al2O3 catalyst showed the highest methyl laurate conversion (73%) and oxygen-containing product selectivity (64%) at 400 °C, LHSV = 1.5 h−1, H2/oil = 500 Nm3/m3, and PH2 = 2.0 MPa over the Ni/La2O3/γ-Al2O3 catalyst. The acidity was favorable to improve the conversion of oils and the yield of alkane products, and the basicity was favorable to obtain oxygen-containing compounds over the corresponding catalysts.

Ni-based catalysts used in heterogeneous catalytic ozonation for organic pollutant degradation: a minireview.

Among various advanced oxidation processes for wastewater treatment, heterogeneous catalytic ozonation (HCO) has a growing interest in pollutant degradation, e.g., pesticides, pharmaceuticals, cresols, detergents, polymers, dyes, and others. Direct oxidation with ozone can occur by this route or indirectly, generating reactive oxygen species through the catalytic activation of the ozone molecule. Then, many catalytic materials were evaluated, such as unsupported and supported oxides, activated carbon, nanocarbons, carbon nitride, and mesoporous materials. This review focuses on the properties and performance of Ni-based catalysts (NiO, supported NiO, Ni ferrites, and M-Ni bimetallic), emphasizing the reaction mechanisms and the importance of the reactive oxygen species in removing toxic organic compounds.

Recent Developments in Dielectric Barrier Discharge Plasma-Assisted Catalytic Dry Reforming of Methane over Ni-Based Catalysts

The greenhouse effect is leading to global warming and destruction of the ecological environment. The conversion of carbon dioxide and methane greenhouse gases into valuable substances has attracted scientists’ attentions. Dry reforming of methane (DRM) alleviates environmental problems and converts CO2 and CH4 into valuable chemical substances; however, due to the high energy input to break the strong chemical bonds in CO2 and CH4, non-thermal plasma (NTP) catalyzed DRM has been promising in activating CO2 at ambient conditions, thus greatly lowering the energy input; moreover, the synergistic effect of the catalyst and plasma improves the reaction efficiency. In this review, the recent developments of catalytic DRM in a dielectric barrier discharge (DBD) plasma reactor on Ni-based catalysts are summarized, including the concept, characteristics, generation, and types of NTP used for catalytic DRM and corresponding mechanisms, the synergy and performance of Ni-based catalysts with DBD plasma, the design of DBD reactor and process parameter optimization, and finally current challenges and future prospects are provided.

La-enhanced Ni nanoparticles highly dispersed on SiC for low-temperature CO methanation performance

For better performances of Ni-based catalysts at low temperatures, Ni/SiC catalyst doped with a little amount of additive La was successfully prepared. The catalytic CO methanation activity tests showed that 3%La–Ni/SiC catalyst was excellent at a low reaction temperature (95.9% CO conversion and 85.1% CH4 selectivity at 250 °C) with a superior stability compared with Ni/SiC (3.4% CO conversion and 0% CH4 selectivity at 250 °C). This can be attributed to that the addition of La can markedly improve the dispersibility of active metal Ni and reduce the particle sizes of Ni nanoparticles or clusters, and can also regulate the interaction between active components and supports. Moreover, the high thermal conductivity and thermal stability could avoid the generation of hot spots in the catalyst bed. These results will promote the development of highly active Ni-based catalysts for the low-temperature methanation reaction.

The Distinctive Effects of Glucose-Derived Carbon on the Performance of Ni-Based Catalysts in Methane Dry Reforming

This study aimed to investigate the effect of carbon derived from glucose (C) on the physicochemical characteristics and catalytic activity of Ni, supported over SiO2, ZSM-5, and TiO2 in methane dry reforming. Among the Ni catalysts without C, Ni/SiO2 exhibited the highest CH4-CO2 conversion and stability at all experimented temperatures. On the other hand, the C-incorporated catalysts prepared by glucose impregnation, followed by pyrolysis, showed dissimilar performances. C improved the stability of Ni/SiO2 in the reforming at 650 °C and 750 °C and increased the CH4 and CO2 conversion to the level close to the thermodynamic equilibrium at 850 °C. However, this element did not substantially affect the activity of Ni/ZSM-5 and exerted a retarding effect on Ni/TiO2. Characterizations with H2-TPD, XRD, EXAFS, and STEM-EDS revealed that the different influences of C by the supports were attributed to the extent of metal dispersion and metal-support interaction.

A comparison of Al2O3 and SiO2 supported Ni-based catalysts in their performance for the dry reforming of methane

Dry reforming of methane (DRM) with CO2 is of great significance in the environmental protection and the utilization of natural gas. SiO2 and Al2O3 are two typical catalyst supports used in DRM. To elucidate the effect of these two supports on the catalytic performance, in this work, Ni/SiO2 and Ni/Al2O3 catalysts are prepared by the incipient wetness method and characterized by BET, TEM, H2-TPR, XRD, TG and Raman technologies. The results indicate that the performance of Ni-based catalyst is closely related to the properties of support and the Ni/SiO2 and Ni/Al2O3 catalysts are rather different in their DRM performance. Ni/SiO2 catalyst exhibits higher initial activity but poor stability; its catalytic activity decreases rapidly in 15 h for DRM at 800°C. Because of the weak metal-support interaction, Ni species on the Ni/SiO2 catalyst is present as large Ni particles, which may promote the formation of coke precursors, viz., the multi-carbon Cn species, leading to the fast carbonaceous deposition and catalyst deactivation. In contrast, the Ni/Al2O3 catalyst displays a lower activity but a much higher stability; its activity in DRM keeps stable in 50 h. Although Ni particles in the Ni/Al2O3 catalyst is much smaller, the strong metal-support interaction promotes the formation of NiAlxOy species during the catalyst preparation process, which may lead to a decrease in the content of active Ni species and give the Ni/Al2O3 catalyst a relatively low catalytic activity in DRM; however, the strong metal-support interaction between Ni and Al2O3 is also of benefit to the formation and stabilization of small Ni particles, which can alleviate the carbanceous deposition and afford the Ni/Al2O3 catalyst a better stability.

Effect of support materials on the performance of Ni-based catalysts in tri-reforming of methane

Tri-reforming of methane (TRM) utilizing CO2, H2O and O2 is an emerging technique for the production of synthesis gas and CO2 abatement. Nevertheless, formulation and design of low-cost, active and stable catalyst for TRM is a major challenge due to its complex reaction network and rapid catalyst deactivation. The support effect is a critical factor influencing the activity and stability of supported Ni catalyst. Thus, a series of supported Ni catalysts over different metal oxides such as Al2O3, ZrO2, TiO2, SBA-15, MgO and CeO2-ZrO2 were prepared. The catalysts were characterized by using N2 - physisorption, XRD, EDX, SEM, TEM, TPR, CO2 – TPD, NH3 – TPD, H2 – pulse chemisorption and TGA. The performance of these catalysts was evaluated at 800 °C, 1 atm, WHSV 17220 mL h−1 g−1 and molar feed composition CH4:CO2:H2O:O2:N2 = 1:0.23:0.46:0.07:0.28 in a fixed-bed reactor. The initial activity of these catalysts followed the order: Ni/Al2O3 > Ni/SBA-15 > Ni/ZrO2 > Ni/CeO2-ZrO2 > Ni/TiO2 > Ni/MgO. Ni/Al2O3 derived from spinel precursor NiAl2O4 resulted in well-dispersed smaller Ni particles, stronger metal-support interaction, a higher degree of reducibility and higher basic sites concentration, which led to its superior activity with 8.72 × 10−2 mmol/gcat·s, 2.31 × 10−2 mmol/gcat·s and 4.2 × 10−2 mmol/gcat·s CH4, CO2, and H2O conversion rate respectively. On the contrary, the stability of SBA-15 and ZrO2 supported Ni catalysts was remarkably high. Hexagonal porous network of SBA-15 confined Ni particles that resulted in high resistance against metal sintering and carbon deposition whereas Ni/ZrO2 offered resistance to Ni re-oxidation owing to its oxophilic property. Experimental investigations reveal that Ni/TiO2 and Ni/MgO resulted in poor CH4, CO2 and H2O conversion rates for TRM due to lower degree of reducibility. Furthermore, Ni/CeO2-ZrO2 catalyst had weak metal-support interaction as observed from TPR studies. Due to larger Ni crystallite size, it exhibited lower conversion compared to Ni/Al2O3, Ni/SBA-15, and Ni/ZrO2.

Influence of metallic promoters on the performance of Ni/SiO2 catalyst in the hydrodeoxygenation of anisole

Ni/SiO2 and Ni-based bimetallic Ni30M/SiO2 catalysts (with a Ni/M atomic ratio of 30; M = Fe, Co, Cu, Zn and Ga) were prepared by the impregnation method and characterized by the means of H2-TPR, XRD, H2 chemisorption, NH3-TPD and N2 sorption; the effect of M promoters on the structure and performance of Ni-based catalysts in the hydrodeoxygenation of anisole was investigated. The results indicated that the metallic promoters have a significant influence on the reducibility of nickel species, due to the interaction between M and Ni species, although the sizes of Ni-M bimetallic crystallites in Ni30M/SiO2 are similar to that of Ni crystallite in Ni/SiO2. Because of the interaction between Ni and M and the enrichment of certain M promoters on the surface of Ni-M bimetallic particles, the adsorption quantity of H2 on Ni30M/SiO2 is lower than that on Ni/SiO2. In addition, the Ni30M/SiO2 catalysts also have more acid sites (especially the weak ones) than Ni/SiO2. For the hydrodeoxygenation of anisole under 300°C, 0.1 MPa, weight hourly space velocity (WHSV) of anisole of 1.0 h−1 and H2/anisole molar ratio of 25, the Ni30M/SiO2 catalysts exhibit lower anisole conversion than Ni/SiO2, probably due to the lower H2 uptakes on the bimetallic catalysts. However, Ni30Ga/SiO2 and Ni30Zn/SiO2 give much higher selectivities to BTX (benzene, toluene and xylene) (81.7% and 76.8%, respectively) than Ni/SiO2 (71.5%). Meanwhile, Ni30Zn/SiO2 exhibits higher activity in methyl transfer and lower activity in C–C bond hydrogenolysis than other catalysts; owing to the high oxophilicity of Zn, from the aspects of increasing carbon yield and reducing H2 consumption, Ni30Zn/SiO2 is probably an appropriate catalyst in hydrodeoxygenation.

Effect of support on the performance of Ni-based catalyst in methane dry reforming

Ni-based catalysts with different supports were prepared and characterized by N2 physisorption, XRD, H2-TPR, H2 chemisorption, and so on; the effect of support on the performance of Ni-based catalyst in methane dry reforming was then investigated. The results indicated that the support has a significant influence on the state of NiO species. SiO2, TiO2 and ZrO2 as a support have a weak interaction with NiO, which facilitates the reduction of the corresponding catalysts; however, the weak interaction may also lead to quick deactivation due to the agglomeration of active metal species. Al2O3 and MgO have a strong interaction with NiO, which may promote the formation of NiAl2O4 spinel and NiO-MgO solid solution, respectively, and make the reduction of corresponding catalysts very difficult. Al2O3 modified by MgO is provided with both proper textural properties and interaction strength between metal and support, which are in favor of the dispersion and stabilization of NiO species. As a result, NiO supported on MgO-modified Al2O3 exhibits superior catalytic performance in methane dry reforming even under very high gas hourly space velocity; it is quite stable during a long term test of more than 100 h.