Ni Dispersion Research Articles

Syngas production through CO2 reforming of propane over highly active and stable mesoporous NiO-MgO-SiO2 catalysts: Effect of calcination temperature

In this contribution, NiO-MgO-SiO2 catalyst was prepared and calcined at different temperatures of 500, 600, 700 and 800 °C. The resulting samples were characterized by BET-BJH, XRD, TPX, CO-chemisorption, EDS and SEM analyses. These were employed toward syngas production via propane dry reforming. The increment in the calcination temperature from 500 to 800 °C decreased the basicity of the catalysts. In addition, the active surface area and Ni dispersion were gradually declined by increasing the calcination temperature from 600 to 700 °C due to active metal sintering during the activation process. The calcined sample at 600 °C displayed the highest propane and CO2 conversions of 93% and 78% at the process temperature of 650 °C, respectively. This satisfying performance was supported through sufficient number of active sites combined with appropriate basic characteristic. Meanwhile, the largest amount of coke deposition was detected upon the calcined samples at 500 and 600 °C while at higher calcination temperatures lower carbon formation was obtained. Eventually, the reaction temperature of 650 °C was determined as the optimum temperature achieving moderately high activity and limited by-product formation over the NiO-MgO-SiO2 material. Ultimately, this mixed oxide catalyst was revealed to be very stable as well.

Highly active Ni/Al2O3 catalyst for CO2 methanation by the decomposition of Ni-MOF@Al2O3 precursor via cold plasma

In this work, a novel Ni/Al2O3-P catalyst for CO2 methanation was prepared via an oxygen plasma decomposition of the Ni-MOF@Al2O3 core–shell precursor. The obtained catalyst showed a higher Ni dispersion (26.5%) and contained less NiAl2O4 spinel when compared with the Ni/Al2O3 prepared by the traditional method. The Ni/Al2O3-P catalyst showed significantly enhanced efficiency toward CO2 methanation as compared with those catalysts with a similar nickel loading but are prepared using the traditional method. For example, the space time yield of methane (STYCH4) of the Ni/Al2O3-P catalyst was as high as 21103.6 mg∙gNi-1∙h−1 at 400 °C and GHSV as 12000 ml∙g−1∙h−1, which is 3.4 times higher than that of the reported catalyst (6190.5 mg∙gNi-1∙h−1) with a similar nickel loading under similar reaction conditions. Moreover, Density Functional Theory (DFT) studies together with the CO2-TPD results revealed that both nickel surface and Ni-Al2O3 interface could activate CO2, while the NiAl2O4 surface could not.

High-Efficiency Hydrogenation of Methyl Furoate to Valuable Methyl Tetrahydrofuran-2-Carboxylate over Ni–SiO2 Catalysts with High Ni Content and Dispersion

High-Efficiency Hydrogenation of Methyl Furoate to Valuable Methyl Tetrahydrofuran-2-Carboxylate over Ni–SiO2 Catalysts with High Ni Content and Dispersion

Slag-based geopolymer microspheres as a support for CO2 methanation

Reducing the emission of CO2 and converting it into energy are the key issues researchers are concerned about. Geopolymers with the advantage of alkali metal synergistic catalysis and excellent ability to adsorb metals are promising catalyst supports. To prove this point, KOH-activated chemically synthesized slag (CaO-MgO-Al2O3-SiO2) and ground granulated blast furnace slag were used as the raw materials in this study to prepare CO2 methanation catalysts. Ni metal (15 wt%) was loaded onto the slag-based geopolymers using the incipient wetness impregnation method. The as-synthesized slag-based geopolymer and real slag-based geopolymer catalysts were prepared and denoted as Ni-P-SGS and Ni-S-SGS, respectively. The results showed that the Ni-P-SGS catalyst showed better Ni dispersion, more alkaline sites, and stronger CO2 adsorption capacity, and hence higher catalytic activity for CO2 methanation than the Ni-S-SGS catalyst. Therefore, the Ni-P-SGS catalyst showed a CO2 conversion of 80.2% and a CH4 selectivity of 99.2% at 400 °C/0.1 MPa and a weight hourly space velocity of 12000 mL g-−1h−1. This performance is superior to that of the Ni-S-SGS catalyst, which showed a CO2 conversion of 72.8% and CH4 selectivity of 98.3%. In addition, the hydrogenation of formate seemed to be the rate-limiting step for the formation of CH4. This work provides sufficient evidence that geopolymers are promising catalyst supports.

Mesoporous nano Ni-Al2O3 catalyst for CO2 methanation in a continuously stirred tank reactor

Mesoporous nano Ni-Al2O3 catalysts were prepared by using Pluronic P123 (P123) and fatty alcohol polyoxyethylene ether (AEO-7) as structure directing agents (SDAs), and applied for CO2 methanation in a continuously stirred tank reactor (CSTR). Compared with NiAl-A prepared by using AEO-7 as SDA and NiAl-N without SDA, NiAl-P prepared by using P123 as SDA possesses ordered mesopores, high Ni dispersion, large metal surface area and amounts of adsorbed CO2, which benefits CO2 conversion. Under the conditions of 1.0 MPa, 300 °C and H2/CO2 ratio of 4, NiAl-P shows the highest CO2 conversion of 74.0% and CH4 yield of 73.6%.

Tri-reforming of methane for syngas production using Ni catalysts: Current status and future outlook

Tri-reforming of methane (TRM) emerged as an attractive approach for syngas production that combines the methane steam reforming (SMR), dry reforming (DRM) and partial oxidation (POX) reactions in a single process. The key merits of the TRM process are the ability to use flue gas directly in the process feedstock, the great flexibility to control the H2/CO ratio for downstream processes, and the relatively lower energy demand and carbon footprint. Considerable progress was achieved over the past decade in catalyst development, process modeling and optimization for syngas production using the TRM process. In this work a critical review of the literature pertaining to Ni-based catalyst development, TRM reaction kinetics, process development, and economics is presented. The use of Ni-based catalysts has received significant attention in recent years; hence this work aims to provide a summary and a critical analysis of the advancement achieved in the design of Ni-based catalysts. Developing active Ni-based catalysts with enhanced resistance to coke formation for the TRM process is anticipated to pave the way for further commercialization ventures. Ni catalysts supported on a wide range of support materials such as Al2O3, CeO2, ZrO2, TiO2, MgO and their mixed oxides are the most widely used catalysts for TRM processes. This review provides a critical analysis of the different attempts made to tune the catalyst properties such as the use of different supports, promotors, and synthesis protocols. Catalyst properties such as Ni dispersion, basicity, Ni particle size, thermal stability is evaluated for various catalytic systems to develop structure-property relationship in TRM processes. Moreover, studies on TRM reaction kinetics, process modeling, and economics are also reviewed. Future outlook in catalysts and process development is also presented in this review to shed lights on the potential pathways to develop TRM processes in an environmentally friendly, and cost-effective manner.

Facile one-pot synthesis of Ni-based catalysts by cation-anion double hydrolysis method as highly active Ru-free catalysts for green H2 production via NH3 decomposition

A series of Ni/Al1CeaOx composites prepared by various synthetic methods, including one-pot anion-cation double hydrolysis (CADH), co-precipitation (CP), CADH followed by wet impregnation (CADH-WI), and CP followed by wet impregnation (CP-WI) were employed as catalysts for ammonia (NH3) decomposition to generate hydrogen. The results revealed that the catalyst prepared by the one-pot CADH method exhibited outstanding catalytic performance (complete NH3 decomposition at around 550 °C) mainly because of significant enhancement in Ni dispersion, Ni reducibility, the quantity of surface oxygen vacancy, and NH3 adsorption affinity. The superior catalytic performance of Ce-containing catalysts over Ni/Al2O3 catalyst was ascribed to the synergistic effects of NiO reducibility, surface oxygen vacancies, basicity, and Ni-support interaction. The selected catalysts demonstrated excellent stability during 100 h continuous operation, without any obvious decrease in NH3 conversion. Overall, the proposed one-pot CADH method offers great advantages in preparing highly active and stable Ni-based catalysts for NH3 decomposition.

Design of coke-free methane dry reforming catalysts by molecular tuning of nitrogen-rich combustion precursors

The valorization of methane and carbon dioxide is a promising solution for mitigating global warming. The dry reforming of methane (DRM) is capable of concomitant conversion of these greenhouse gases into starting materials for production of synthetic fuels, promoting a carbon neutral avenue for fuel production. The development of efficient, stable, and economic catalysts presents a challenge owing to the comparatively rapid deactivation of DRM catalysts under reaction conditions. Here, Ni/La2O3 DRM catalysts are prepared by combustion synthesis of Ni and La complexes of nitrogen-rich precursors. We expound the relationship between structures of the combustion precursors, the thermochemistry of their combustion, the structures of the resultant Ni/La2O3 catalysts, and their performance under DRM conditions. We show that the best catalyst is derived from energetic precursor which has the sharpest exotherm and rapidly releases the largest amounts of nitrogen gas. These properties give rise to the crystallization of the Ni/La2O3 catalyst with high Ni dispersion and strong metal-support interactions. This work can act as starting point to expand the link between the chemistry of combustion precursors and the resulting catalyst properties, eventually realizing the rational design of high-performance catalysts prepared by combustion synthesis through tailoring the chemistry and structure of the nitrogen-rich precursors.

Effect of pore structure on Ni/Al2O3 microsphere catalysts for enhanced CO2 methanation

An understanding of the support effect is fundamental for guiding the rational design of heterogeneous catalysts. Herein, the role of pore structure on metal dispersion and catalytic performance was comprehensively investigated using Ni/Al2O3 catalysts. Three different Al2O3 supports, including Al2O3 microspheres prepared in microchannels and two commercially available Al2O3 supports named Sample 1 and Sample 2, were used and the Ni/Al2O3 catalysts were prepared by wetness impregnation method. X-ray diffraction, transmission electron microscopy, H2 temperature-programmed reduction, X-ray photoelectron spectroscopy, N2 adsorption–desorption, and H2 pulse chemisorption analyses combined with a sintering kinetic model were used to investigate the effect of the support pore structure. The narrow pore size distribution (3–15 nm) of Al2O3 microspheres and Sample 1 led to a uniform NiO dispersion for the calcined catalysts. Moreover, the high specific surface area (291 m2/g) and large pore volume (1.0 mL/g) of the Al2O3 microspheres were beneficial for the deposition of NiO particles inside mesopore to obtain a stronger metal–support interaction. Owing to the smaller NiO nanoparticles and stronger metal–support interaction, the reduced Ni/Al2O3 microspheres exhibited an average Ni particle size of 10.2 nm under 36 wt% nickel loading, whereas the average Ni particle size loaded on Sample 1 and Sample 2 were 12.6 nm and 13.2 nm, respectively. The optimized CO2 conversion of 87.0% at 300 °C under atmospheric pressure was attributed to the large pore volume and uniform Ni dispersion of Ni/Al2O3 microsphere catalysts while the same value for Sample 1 and Sample 2 catalysts was 81.5% and 55.0%, respectively. This work provides valuable guidelines for designing effective CO2 methanation support and proves the potential application of Al2O3 microspheres for CO2 methanation.

Restructuring Ni/Al2O3 by addition of Ga to shift product selectivity in CO2 hydrogenation: The role of hydroxyl groups

Ni/Al2O3 is an active catalysts for CO2 hydrogenation to both CH4 and CO. By doping with Ga, we succeeded in shifting the selectivity of these catalysts almost completely toward CO. In-situ IR spectroscopy studies showed that the catalyst activity is directly related to the concentration of surface hydroxyl groups that are responsible for the adsorption of CO2 and the formation of intermediate bicarbonates and formates on the catalyst surface. The addition of Ga improved the Ni dispersion which was concomitant with the formation of a Ni-Ga layer on the surface of alumina, thereby reducing the surface hydroxyl concentration. The reduced and weakened interaction between the intermediate products, i.e. bicarbonates and formates, and the catalyst surface, increased the CO selectivity from ∼40 % to 98 %.

Boosting CO2 reforming of methane via the metal-support interaction in mesostructured SBA-16-derived Ni nanoparticles

High surface area and porosity SBA-16 was synthesized and used as support for Ni nanoparticles using three methods including wet impregnation, citric acid-assisted impregnation, and ammonia evaporation. All the studied samples showed high activity in the CO2 reforming of methane reaction, however, the best catalytic behavior was found for the catalyst derived from ammonia evaporation. Based on characterization techniques, it was assumed that the improvement in Ni/SBA-16-AE performance was due to the strong metal-support interaction resulting from the formation of Ni-phyllosilicate. Additionally, a high Ni dispersion was observed which may be related to the confinement of cage-like pores of the SBA-16 matrix. The ammonia evaporation technique can well contribute to the limited sintering of Ni nanoparticles and reduced amount of deposited carbon.

Enhancing resistance of carbon deposition and reaction stability over nickel loaded fibrous silica-alumina (Ni/FSA) for dry reforming of methane

Syngas production from the dry reforming of methane is now the most extensively utilized method for removing massive amounts of greenhouse emissions. Effective solutions towards the utilization of greenhouse gases such as CO2 and CH4 are scarce, except for power generation in the energy sector, which is a major source of CO2. Herein, dry reforming of methane was experimented for the first time using an effective catalytic system composed of 5% Ni fibrous silica-alumina (FSA) that was successfully fabricated using a hydrothermal method. The characterization results from XRD, FESEM mapping, TEM, BET,XRF, FTIR, H2-TPR, TGA/DTA, and Raman spectra demonstrated that Ni/FSA is composed of orderly Ni dispersion, small particles of Ni, robust basic sites, and high oxygen vacancies which enhanced the catalytic efficiency. The synthesized Ni/FSA also reduced coke formation and had long-term stability with no evidence of inactivation during and after the catalytic cycles. The superior activity of Ni/FSA was manifested in the high conversion rates of CH4 and CO2 at 97% and 92% respectively, with a H2:CO ratio of ≈ 1. The stability of Ni/FSA was also sustained over 30 h of operation at 800 °C. The findings of the Raman, TEM, and TGA/DTA tests revealed that the spent Ni/FSA catalysts did not exhibit graphitic carbon or metal sintering in significant amounts when compared to commercial Ni–Si/Al catalysts.

Structural effect of Ni/TiO2 on CO methanation: improved activity and enhanced stability.

CO methanation over a supported Ni catalyst has attracted increasing attention for its applications in synthetic natural gas production, CO removal for ammonia synthesis and fuel cells, among others. However, the deactivation of the Ni catalyst caused by sintering and carbon deposition hinders further application of the Ni catalyst. The activity of Ni catalysts needs further improvement as well. In this work, the structural effect of the Ni/TiO2 catalyst on CO methanation was investigated. A plasma decomposition, initiated at room temperature and operated around 150 °C, of the nickel precursor was applied to prepare the catalyst. Compared to the thermally decomposed Ni/TiO2 catalyst, the plasma-decomposed catalyst shows improved activity with enhanced stability. The catalyst characterization shows that the plasma-decomposed Ni/TiO2 catalyst possesses smaller Ni particle size and higher Ni dispersion, resulting in improved coke resistance and enhanced anti-sintering ability for CO methanation. The present study confirms that a catalyst with good activity for CO methanation possesses good activity for CO2 methanation as well, if the CO2 methanation takes the CO methanation pathway.

Syngas production by methane tri-reforming: Effect of Ni/CeO2 synthesis method on oxygen vacancies and coke formation

The CH4 tri-reforming process can contribute to mitigating CO2 emissions and enables the formation of syngas with different H2/CO ratios. Ni catalysts supported on CeO2 were synthesized by hydrothermal and ionothermal methods and were applied in methane tri-reforming reactions with GHSV of 48,000 mL/g.h, at atmospheric pressure and temperature of 800 °C. The catalytic activity in the tri-reforming reaction was enhanced by changing the morphological properties of the catalyst by appropriate selection of the amount of ionic liquid used in the synthesis procedure. Changing the composition resulted in methane conversion increasing from 60 % to 95 % and carbon dioxide conversion increasing from 40 % to 55 %. Increased Ni dispersion was related to the oxygen vacancies on the Ni-Ce surface, which created interfacial active sites. The results of XANES combined with XPS revealed that a partial reduction of Ni species contributed to high hydrogen yields, due to the distribution of active sites over the catalyst surface. These sites remained active during 5 h, demonstrating the positive effect of the ionic liquid used in the CeO2 synthesis. In addition, post-reaction characterization results showed Ni re-oxidation on the ceria support produced without ionic liquid.

Electrospun nanofibrous Ni/LaAlO3 catalysts for syngas production by high temperature methane partial oxidation

Ni/Al2O3 catalysts have been widely used for methane reforming while the formation of NiAl2O4 with low reducibility reduces catalyst efficiency. La2O3 was used to promote the catalytic activity of Ni/Al2O3 catalysts through improving Ni dispersion. LaAlO3 perovskite showed catalytic activity in methane coupling and also used as a catalyst support for methane reforming. This study systematically investigated the effect of La2O3 addition into Ni/Al2O3 catalysts and found the formation of LaAlO3 perovskite played an important role, which requires high crystallization temperatures. The thermally-stable structure of nanofibrous catalysts was employed to develop high-performance Ni/LaAlO3 catalysts. High calcination temperature resulted in the enhanced crystallinity of LaAlO3 perovskite, improved Ni reducibility and strengthened catalyst/support interaction, which contributed to high catalytic performance during methane partial oxidation. The Ni/LaAlO3 catalyst calcined at 1100 °C generated a CH4 conversion of 91.2% during methane partial oxidation with H2 and CO selectivities of 95.5% and 92.4%, respectively. It is because La2O3 addition into Ni/Al2O3 promoted Ni reduction via forming LaAlO3. Therefore, an efficient and thermally-stable fibrous Ni/LaAlO3 catalyst has been developed for high temperature methane partial oxidation.

Synergistic effect of freeze-drying and promoters on the catalytic performance of Ni/MgAl layered double hydroxide

Methane dry reforming is a potentially useful reaction but possesses some disadvantages such as catalyst deactivation by coking. Some new freeze-dried promoted-Ni/MgAl catalysts were used in this work for solving this drawback. The synergic effect of the freeze-drying method and incorporation of promoters was studied on physicochemical features of catalysts and catalytic performance. Field emission scanning electron microscopy images (FE-SEM) and high-resolution transmission electron microscopy (HR-TEM) revealed that the Sr-promoted Ni/MgAl catalyst had a scaffold structure with desirable pores in contact with feedstock gases. The temperature-programmed reduction (H2-TPR) and temperature-programmed deposition (CO2-TPD) techniques confirmed that the reduction behavior and basicity of the catalysts are affected by the type of promoter. In comparison to Y and Sr-promoted catalysts, the Sr-Ni/MgAl catalyst with the lower reduction temperatures, smaller Ni crystallite size, greater Ni dispersion, and higher basicity had the highest catalyst activity (72% CH4 conversion) and stability after 20 h time on stream without any carbon deposition. The higher basic cites resulted in eliminating coke specimens from the catalyst surface.

Insight into the anti-coking ability of NiM/SiO2 (M=ZrO2, Ru) catalyst for dry reforming of CH4 to syngas

The development of Ni-based catalysts with outstanding anti-coking ability is necessary for realizing the industrial application of dry reforming of CH4 (DRM) to syngas. Here, a facile combustion method with unique characteristic was employed to prepare the Ni/SiO2 catalyst with different promoters (ZrO2 or Ru). The effects of Ni particle size and promoter (ZrO2 or Ru) on the anti-coking ability of Ni/SiO2 catalyst were examined. The XRD and TEM results showed that improved Ni dispersion can be obtained via the facile combustion method, accompanying with enhanced metal-support interaction and CO2 adsorption capacity confirmed by H2-TPR and CO2-TPD, respectively. In comparison with Ni-IMP catalyst (prepared via the traditional impregnation method), the carbon deposition over Ni–C catalyst (prepared via the combustion method) decreased by 67% (from 2.7 to 0.9 mg carbon deposition·g−1CH4) as a result of the small Ni particles. The H2-TPR and XPS results revealed the interaction between promoter (ZrO2 and Ru) and Ni. The addition of ZrO2 can enhanced the CO2 activation ability of catalyst and the formed oxygen species can facilitate the elimination of carbon species, further decreasing the carbon deposition compared with Ni–C catalyst. The best catalytic performance with least carbon deposition (only 0.4 mg carbon deposition·g−1CH4) is achieved on the NiRu–C catalyst. The slower CH4 dissociation rate and the improved CO2 activation benefited from Ru can bring in the better balance between the carbon formation and elimination, leading to the best anti-coking ability of catalyst.

Deoxygenation of non-edible fatty acid for green diesel production: Effect of metal loading amount over Ni/MgO–Al2O3 on the catalytic performance and reaction pathway

Ni/MgO-Al2O3 (Ni/MG70) catalysts were developed for the deoxygenation reaction to produce green diesel from non-edible fatty acids. As the Ni loading amount was increased from 5% to 30%, the characteristics of the catalysts, such as Brunauer–Emmett–Teller (BET) surface area, Ni dispersion, reducibility, number of Ni active sites, and acidity, varied. Among the prepared catalysts, the 20% Ni/MG70 catalyst showed excellent deoxygenation performance owing to its highest number of Ni active sites, easier reducibility, and appropriate acidity. Furthermore, it was confirmed that deoxygenation in this study was carried out via the hydrodeoxygenation reaction pathway to remove oxygen species as H2O. In addition, the basic fuel properties, calorific value and viscosity, were analyzed for produced green diesel.

Ni/CeO2 prepared by improved polyol method for DRM with highly dispersed Ni

AbstractDry reforming of methane (DRM) of Ni‐based catalysts is a hot method to solve greenhouse gas problems. The improved polyol method could overcome the disadvantage of Ni agglomerate sintering by the impregnation method. In this work, Ni/CeO2 catalysts were prepared by an improved polyol method with different CeO2 support and applied for methane dry reforming, which showed excellent catalytic activity and stability. The X‐ray power diffraction (XRD), transmission electron microscopy (TEM), X‐ray photoelectron spectra (XPS), H2 temperature‐programmed reduction (H2‐TPR) were used to study the composition of Ni species, the Ni‐CeO2 interaction, and Ni dispersion, while textural properties, oxygen vacancy, and the behavior of CO2 adsorption and activity were research by N2 adsorption and desorption, Raman and CO2‐TPD. There in, Ni/CeO2‐R showed excellent catalytic activity (CH4 and CO2 conversion: 61.8% and 96.5%; H2/CO radio: 0.93) and remained stable after the 50‐hr stability test. Meanwhile, the formation and graphitization of deposited carbon were observed and studied by XRD, Raman, TG/DTA, and TEM, and the cause of the deactivation of the catalyst was analyzed. This work studied and demonstrated the advantages of the improved polyol method and the differences between different CeO2 supports and provided a new idea for the construction of the catalyst for methane dry reforming. © 2021 Society of Chemical Industry and John Wiley & Sons, Ltd.

Utilization of palm oil fuel ash (POFA) as catalyst support for methane decomposition

An agricultural waste, palm oil fuel ash (POFA) has been evaluated as a Ni catalyst support for the methane decomposition process. The effects of solvent and pre-treatment technique during the POFA pre-treatment have been investigated towards the catalytic performance of Ni supported on POFA (Ni-POFA) catalyst prepared at 10 wt% Ni loading. Methane decomposition of Ni-POFA catalyst was carried out at 550 °C for 6 hrs. The POFA and Ni-POFA were characterized using X-ray fluorescence (XRF), X-ray diffractometer (XRD), N2 adsorption–desorption isotherms and field emission scanning electron spectroscopy (FESEM). The results showed that citric acid solution was the best solvent for POFA pre-treatment. The SiO2 content in the POFA pre-treatment improved from 42.4 to 72 wt%. Good CH4 conversion achieved by Ni-POFA catalyst in the methane decomposition was attributed to high SiO2 in the POFA treated with citric acid. Compared to conventional stirring, pre-treatment of POFA with ultra-sonication technique has produced POFA support with smaller particles size, and Ni-POFA catalyst with better BET surface area and better Ni dispersion. These catalyst properties have contributed to an exceptional catalytic performance of 71% of initial CH4 conversion and 4.2% of initial H2 yield of Ni-POFA catalyst in the methane decomposition. The work suggests that POFA has the potential to be utilized as catalyst support, and pre-treatment is crucial for a reasonable catalytic performance in methane decomposition.