New performing hydroxyapatite-based catalysts in dry-reforming of methane

Dry reforming of methane (DRM) is a promising process for the production of synthetic gas from carbon dioxide and methane. However, the design of a performing catalyst for this reaction is still challenging since catalyst deactivation usually takes place, principally by thermal sintering at high temperatures (700–950 °C) and by carbon deposition. In this work, calcium hydroxyapatite (HAP) and HAP-doped magnesium (Mg_HAP) supported nickel catalysts were synthesized by wet precipitation method, characterized by various physico-chemical and thermal techniques, and evaluated in DRM reaction. Outstanding catalytic performance in DRM could be obtained with Ni/ HAP and Ni/Mg_HAP catalysts, thanks to a tunable acidity-basicity of these supports, a strong metal-support interaction, and a good thermal stability of nickel nanoparticles. H₂ and CO were the main products, with stable selectivity up to 85 ∓ 3%, while H₂O and solid carbon were byproducts with 5–10% of selectivity.     

Boron-doped Ni/SBA-15 catalysts with enhanced coke resistance and catalytic performance for dry reforming of methane

Nickel-based heterogeneous catalysts have shown promising results in many industrial-scale catalytic reforming processes and hydrocarbon reforming reactions such as dry reforming of methane (DRM). However, it is also reported that Ni-based catalysts generally show less resistance to the carbonaceous deposition, which ultimately causes their rapid deactivation during the reaction. One possible solution to improve the coke resistance is the addition of a promoter to the catalyst, which has shown successful results to reduce the coke formation. Therefore, this study also aimed to prepare boron-promoted Ni-based catalysts and investigate their efficiency for DRM reactions. A series of different catalysts with 10% nickel and x% boron (x: 1%, 2%, 3%, and 5%) were prepared by using an ordered mesoporous silica as a support and tested in DRM. The results demonstrated that boron-promoted Ni/SBA-15 catalysts obtained significant catalytic activity for CH₄ and CO₂ conversions. Meanwhile, it was noticed that a lower concentration of boron (1 and 2%) was more favourable to achieve higher catalytic activity, whereas the higher concentration (3% and 5%) resulted in a comparatively lower conversion for CH₄ and CO₂. Evidently, the higher activity of 2% B-promoted catalyst was ascribed to the synergistic effect of high surface area and lower crystallite size that greatly improved the active sites accessibility. Moreover, the results confirmed 14% carbon deposition on unpromoted (NS) catalyst and it was reduced to 1.3% for 2% boron-promoted catalyst owing to the presence of B-OH species on catalyst surface.     

Improved performance of Ni/Al2O3 catalyst deriving from the hydrotalcite precursor synthesized on Al2O3 support for dry reforming of methane

Exploiting Ni-based catalysts with excellent catalytic activity and anti-coking ability is significant for dry reforming of CH₄ with CO₂ (DRM) which is a promising route to CO₂ utilization. In this work, the Ni/Al₂O₃ catalyst with hydrotalcite precursor (NiAl-LDH) was synthesized by a facile in-situ growth method. And the effect of the NiAl-LDH structure on the catalytic activity and anti-coking ability of Ni/Al₂O₃ catalyst was revealed. The H₂-temperature programmed desorption (H₂-TPD) revealed that better Ni dispersion and more Ni–Al₂O₃ interface could be obtained by the NiAl-LDH precursor, which were vital for the activation of CH₄ and CO₂. Moreover, the NiAl-LDH precursor with non-LDH phase or turbostratic structure was also created by insufficient or extra amount of urea, and the obtained catalysts exhibited a poor catalytic stability, further confirming the importance of the LDH structure. In comparison with the Ni-IMP catalyst prepared by the conventional impregnation method, the CH₄ conversion increased by 16% and the carbon deposition decreased by 75% over Ni-6 catalyst with well-organized LDH precursor under the same reaction conditions. Hence, this work represents an important step toward developing Ni-based catalysts with excellent catalytic activity and anti-coking ability for DRM with the LDH precursor.     

Glycine-assisted preparation of highly dispersed Ni/SiO2 catalyst for low-temperature dry reforming of methane

Ni-based catalysts have been widely studied in reforming methane with carbon dioxide. However, Ni-based catalysts tends to form carbon deposition at low temperatures (≤600 °C), compared with high temperatures. In this paper, a series of Ni/SiO₂-XG catalysts were prepared by the glycine-assisted incipient wetness impregnation method, in which X means the molar ratio of glycine to nitrate. XRD, H₂-TPR, TEM and XPS results confirmed that the addition of glycine can increase Ni dispersion and enhance the metal-support interaction. When X ≥ 0.3, these catalysts have strong metal-support interaction and small Ni particle size. The Ni/SiO₂-0.7G catalyst has the best catalytic performance in dry reforming of methane (DRM) test at 600 °C, and its CH₄ conversion is 3.7 times that of Ni/SiO₂-0G catalyst. After 20 h reaction under high GHSV (6 × 10⁵ ml/g_cat/h), the carbon deposition of Ni/SiO₂-0.7G catalyst is obviously lower than that of Ni/SiO₂-0G catalyst. Glycine-assisted impregnation method can enhance the metal-support interaction and decrease the metal particle size，which is a method to prepare highly dispersed and stable Ni-based catalyst.     

Carbon nanofibers decorated SiC foam monoliths as the support of anti-sintering Ni catalyst for methane dry reforming

A silicon carbide (SiC) foam monolith decorated with a carbon nanofibers (CNFs) layer was employed as the catalyst support for Ni-based catalyst preparation, used for the CO₂ dry reforming of methane (DRM) reaction. The loading amount of CNFs on the SiC foam monolith was 6.6 wt.%, which obviously increased the surface area of the pristine SiC foam from 4 m²/g to 24 m²/g. The prepared CNFs layer strongly attached to the pristine SiC surface and was considerably stable even after 100 h time on stream (TOS) DRM reaction. The CNFs decorated SiC composite support provided more anchorage sites for improving the dispersion of the Ni particles and enhanced the metal-support interaction compared to the pristine SiC support. Compared with other catalysts such as Ni/SiC and Ni/CNFs, the Ni/CNFs-SiC catalyst exhibited not only the highest activity but also remarkable stability during DRM reaction. The XPS and SEM-EDS results showed that the carbon deposition over the nickel surface of Ni/CNFs-SiC catalyst was much less than those of Ni/SiC and Ni/CNFs catalysts. In addition, the XRD analysis verified that almost no sintering of nickel particle was detected over the Ni/CNFs-SiC catalyst, which was prepared with CNFs-SiC composite as catalyst support, even after 100 h TOS DRM reaction at 750 °C.     

Lanthanoid-containing Ni-based catalysts for dry reforming of methane: A review

Dry reforming of methane (DRM) is known to produce synthesis gas through the utilization of greenhouse gases to ensure environmentally benign process and rational use of natural resources. Many catalyst formulations operating at “ideal” conditions were proposed for DRM reaction, including those based on noble (Pt, Rh) and non-noble (Ni, Co) metals supported on various oxides. This review is focused on the recent advances in lanthanoid-containing Ni-based DRM catalysts. We consider the performance of Ni-based catalysts supported on LnO_x oxides (La₂O₃, CeO₂, etc.), promotion of the said composites by noble or transition metals, organization of pristine and promoted Ni–LnO_x interfaces on the surfaces of various supports, including ordered materials. Analysis of features of the high-performance DRM catalysts is provided. The outlook of the existing challenges and opportunities in the rational design of a new generation of lanthanoid-containing Ni-based catalysts for dry reforming of methane and other hydrocarbons is provided.     

Catalytic performance of dioxide reforming of methane over Co/AC-N catalysts: Effect of nitrogen doping content and calcination temperature

The nitrogen doped activated carbon (AC-N) has been successfully prepared with commercial activated carbon as carbon material followed by a simple N-doping method using melamine as nitrogen sources. Using AC-N as the supports, cobalt supported on N-doped activated carbon (Co/AC-N) were developed and used as catalyst for dry reforming reaction (DRM). It was discovered that the Co/AC-N catalysts revealed much higher catalytic performance for DRM reaction in comparison to activated carbon supported cobalt catalyst (Co/AC). Moreover, the catalytic activity was influenced by preparation conditions of AC-N such as calcination temperature and the doping amount of nitrogen. The catalysts were characterized by BET, XRD, XPS, H₂-TPR, Raman spectroscopy and TEM. It was found that catalytic activities of the catalysts with different calcination temperature and nitrogen doping were influenced by catalyst surface defects and disorders, Co²⁺/Co³⁺ molar ratio, the content of nitrogen function groups (graphitic N, pyrrolic-N and pyridinic-N) and interaction between active metal and support. The Raman spectroscopy illustrated that the N-doped catalyst surface defects and disorders increased, which improved the performances of the Redox catalysts. The XPS valence band also revealed that higher Co²⁺/Co³⁺ molar ratio and nitrogen function groups was achieved by decreasing calcination temperature and increasing nitrogen doping. In short, the doping of nitrogen increased the structural defects and the interaction between active metals and supports, modified the surface electronic structure, which were facilitated the oxidation and reduction of methane and carbon dioxide.     

Hollow hierarchical Ni/MgO-SiO2 catalyst with high activity,thermal stability and coking resistance for catalytic dry reforming of methane

The methane dry reforming (DRM) simultaneously converts the two greenhouse gases and produces syngas (CO + H₂), which is being significant for both environmental and industrial consideration. Employing well-defined crystal oxides as precursors can produce Ni-based DRM catalysts with good sintering and coking resistance by enhancing the metal-support interactions. Adding basic promoters also is considered as an effective way to improve the coking resistance of DRM catalysts, although challenge remains in the control over the structure, morphology and interaction of the promoter in the catalyst. To well combine the two methods together for better catalytic performance, in this work a Ni/MgO-SiO₂ catalyst was synthesized through a facile one-pot hydrothermal process, during which Ni-phyllosilicate formed as the precursor of Ni particles and MgO promoter was generated in form of Mg-phyllosilicate. This Ni/MgO-SiO₂ had a hierarchical hollow sphere structure with large surface area (477.4 m²/g). Both the Ni particles (avg. 6.0 nm) and MgO promoter uniformly distributed. This hollow hierarchical catalyst performed high activity, thermal stability and coking resistance for catalytic dry reforming of methane.     

Highly active Nd-promoted Ni@Al2O3 core-shell catalyst for steam reforming of acetic acid: Insights of the remarkable coke resistance

Aiming at enhancing the coke resistance of Ni-based catalysts, the Nd-doped Ni@A₂O₃ core-shell catalysts were prepared and their catalytic performance was evaluated in the steam reforming of acetic acid (SRAA). The catalysts were characterized by BET, XRD, XRF, HRTEM, H₂-TPR, NH₃-TPD, and DTG. The catalytic performance was greatly enhanced by the incorporation of Nd, with decreased yields of CO, CH₄, and acetone, increased yield of CO₂, and remarkable carbon resistance. The decoking behavior of the spent catalyst was elucidated by H₂O¹⁸-TSD. A low reaction temperature facilitates the formation of amorphous carbon, leading to catalyst deactivation. The decoking ability of the catalyst is greatly improved by the Nd incorporation but is also catalyzed by the exposed Ni surface. The Ni0.01Nd@Al catalyst greatly balanced the exposed Ni surface and the mobile lattice oxygen, showing the highest catalytic activity, lowest coke deposition, and superb decoking ability.     

Steam reforming of toluene as a tar model compound with modified nickel-based catalyst

Catalytic steam reforming is a promising route for tar conversion to high energy syngas in the process of biomass gasification. However, the catalyst deactivation caused by the deposition of residual carbon is still a major challenge. In this paper, a modified Ni-based Ni-Co/Al₂O₃-CaO (Ni-Co/AC) catalyst and a conventional Ni/Al₂O₃ (Ni/A) catalyst were prepared and tested for tar catalytic removal in which toluene was selected as the model component. Experiments were conducted to reveal the influences of the reaction temperature and the ratio between steam to carbon on the toluene conversion and the hydrogen yield. The physicochemical properties of the modified Ni-based catalyst were determined by a series of characterization methods. The results indicated that the Ni-Co alloy was determined over the Ni-Co/AC catalyst. The doping of CaO and the presence of Ni-Co alloy promoted the performance of toluene catalytic dissociation over Ni-Co/AC catalyst compared with that over Ni/A catalyst. After testing in steam for 40 h, the carbon conversion over Ni-Co/AC maintained above 86% and its resistance to carbon deposition was superior to Ni/A catalyst.     

Dry reforming of methane to syngas over lanthanum-modified mesoporous nickel aluminate/γ-alumina nanocomposites by one-pot synthesis

La-modified NiAl₂O₄/γ-Al₂O₃?La composites with mesoporous structures were prepared by one-pot template-free strategy and applied for dry reforming of methane (DRM) to syngas. The characterization results confirmed that these materials possessed high specific surface areas, large pore volumes and narrow pore size distributions. The reduced catalysts exhibited excellent catalytic properties as well as long-term stability for DRM reaction. Addition of La showed little influence on the catalyst structure and the mean sizes of metal Ni particles, but could enhance the medium-strength basicity and the accumulation of Ni²⁺ on the catalyst surface, resulting in the enhancement of intrinsic activity, the reduction of apparent activation energy, and the suppression of carbon deposition for DRM reaction. The catalyst containing 3 wt% La possessed the best catalytic performance. The characterization of spent catalysts also demonstrated that La could effectively prevent the phase transformation of γ-alumina in the DRM process.     

Synthetic gas production by dry reforming of methane over Ni/Al2O3–ZrO2 catalysts: High H2/CO ratio

Alumina prepared by the sol-gel method, was impregnated with zirconia (5, 15 and 30 wt.%). Subsequently, the resulting Al₂O₃–ZrO₂ supports were impregnated with 15% Ni to obtain the Ni/Al₂O₃–ZrO₂ catalysts. The obtained catalysts were characterized by BET, SEM, XRD, H₂-TPR and TPD- CO₂. The catalytic activity was studied by means of dry reforming of methane (DRM) for syngas production. The catalysts displayed different physicochemical properties and trends of their catalytic activity as a function of the ZrO₂ content in the mixed oxide supports. For instance, ZrO₂ (5 wt %) in the catalyst, led to enhanced concentration of the medium strength basic sites and increased specific surface area, yielding thus the best performance in the DRM, with low carbon deposition after 36 h of reaction, compared with the other catalysts. This indicates that during the DRM reaction, this catalyst can provide more surface oxygen to prevent carbon deposits that could deactivate the catalyst.     

Effective suppression of deactivation by utilizing Ni-doped ordered mesoporous alumina-supported catalysts for the production of hydrogen and CO gas mixture from methane

Several different kinds of ordered mesoporous alumina (OMA)-supported and Ni-doped OMA-supported Ni catalysts have been prepared for catalytic partial oxidation of methane (CPOM) to produce hydrogen and CO gas mixture. The Ni metal was incorporated in various ways of the impregnation, the doping, and the partial doping followed by impregnation. The prepared OMA-supported catalysts showed a wormhole-like, pseudo-hexagonal structure. By incorporating Ni in the OMA matrix during synthesis of supports, the resulting catalysts showed better-distributed and less-sintered nanocrystals even after CPOM at elevated temperature for over 100 h. By employing the partial doping of Ni followed by impregnation of Ni, the prepared CPOM catalyst was found more productive due to the well-distributed and well-anchored Ni nanocrystals inside the OMA matrix and the confined ordered mesopores as well. Through the test under non-stoichiometric feed ratio, the catalyst prepared only by impregnation was found vulnerable to carbon deposition and deactivated more rapidly. Even worse, the formation rate of carbon deposition was so fast that the test could not be conducted due to the increased pressure difference. In contrast, the highly distributed Ni nanocrystals partially or fully utilizing doping were found to have stronger resistance to carbon deposition.     

Hydrogen production from catalytic steam reforming of biomass pyrolysis oil or bio-oil derivatives: A review

Steam reforming of biomass pyrolysis oil or bio-oil derivatives is one of the attractive approaches for hydrogen production. The current research focused on the development of promising catalysts with favorable catalytic activity and high coke resistance. Noble metal such as Rh has been proven to achieve promising reforming reaction efficiencies. However, Ni has attracted considerable attention owing to its stability, cost effectiveness, and good activity in breaking C–C and C–H bonds. Nevertheless, Ni-based catalysts have serious carbon deposition problems arising from chemical poisoning, metal sintering, and poor metal dispersion. This paper attempted to review the current trends in catalyst development considering the aspects of supports, metals, and promoters as an effort to find possible solutions for the limitations of Ni-based catalysts. The present review also covered the current understanding on the reaction mechanisms as well as the future prospects in the field of steam reforming catalysts.     

Titanium nitride promoted Ni-based SBA-15 catalyst for dry reforming of methane

Titanium nitride (TiN) promoted nickel catalysts were synthesized and employed as an alternative catalyst in dry reforming of methane (DRM). The series of this catalyst containing various amount of Ni and TiN was prepared in two steps, direct synthesis of SBA-15 in the presence of TiN and the impregnation of Ni. The influence of Ni and TiN loading on DRM reaction was investigated using a feed ratio of CH₄/CO₂ = 1, at 700 °C and atmospheric pressure for a duration of 4 h. The promising catalysts, that gave the highest feed conversions and product yields, were selected for further investigation, compared to non-promoted Ni catalyst using the same conditions but for 12 h of reaction. The results showed that the performance of Ni catalyst was improved by the incorporation of TiN. The modified catalysts provided not only high catalytic activity but also enhancement of coke resistance.     

Highly dispersed Fe-decorated Ni nanoparticles prepared by atomic layer deposition for dry reforming of methane

Dry reforming of methane (DRM) is a sustainable chemical process that can simultaneously transform methane and carbon dioxide, which are generally considered greenhouse gases, into syngas with H₂/CO ratio close to 1. The deposition of carbon on the active sites during long-period DRM tests will lead to severe deactivation of Ni-based catalysts. Thus, in this work, we proposed a series of uniformly dispersed Fe-decorated Ni/Al₂O₃ catalysts via atomic layer deposition (ALD) to solve this key issue. Modification with trace amounts of Fe (0.3–0.6%) had multiple effects on facilitating the CH₄ dissociation on Ni⁰, improving the low-temperature catalytic activity, moderating the carbon species and accelerating coke oxidation. The sample denoted as 0.3%Fe/Ni/Al₂O₃ exhibited almost no activity loss in the 72 h test at 650 °C. The Fe-decorated Ni/Al₂O₃ structure achieved a balance between the enhancement of CH₄ cracking and the elimination of coke. Furthermore, this advanced ALD approach of preparing uniform secondary metal nanoparticle-decorated catalysts provided guidance to other bimetallic systems, such as Pt/Ni, Mn/Ni, and Cu/Ni.     

The reconstruction of Ni particles on SBA-15 by thermal activation for dry reforming of methane with excellent resistant to carbon deposition

The improved Ni/SBA-15 catalysts were prepared by thermal inducing method and applied to dry reforming of methane. The promoting effect exerted by thermal activated reconstruction was studied systematically by means of various characterization techniques. TEM results indicated that the thermal inducing process led to the reconstruction of Ni particles to form ultra-fine Ni nanoparticles (2–3 nm) uniformly distributed on SBA-15. The resulting Ni nanoparticles not only improved catalytic activity but also inhibited the formation of carbon deposition during the DRM reaction. The thermal treatment catalyst with tiny particles presented the superior catalytic performance in the DRM reaction, where H₂/CO ratio was close to 1 and no deactivation was discovered after continuous reaction at 750 °C for 50 h. Additionally, it was found that the metal-support interaction was strengthened observably after the thermal activated reconstruction. The strong interaction anchored Ni particles to prevent their high temperature sintering, thus forming stable catalytic centers. Therefore, the conversions of both CO₂ and CH₄ almost stabilized at 90% and 85%, respectively, for the thermal activated reconstruction samples during the long-term catalytic test.     

Engineering of Pt-based nanostructures for efficient dry (CO2) reforming: Strategy and mechanism for rich-hydrogen production

Dry (CO₂) reforming of methane (DRM) is of great interest in scientific, environmental, and industrial applications. The high-energy stationary path DRM provides gigatons of CO₂ utilization to produce syngas (CO and H₂), which is used to form a wide range of valuable chemicals and products through Fischer-Tropsch process. Numerous fences remain in the DRM including the absence of durable, effective, and economically viable catalysts that maintain outstanding catalytic performance along with deactivation resulting from carbon deposition. Pt-based catalyst is highly auspicious for DRM with a substantial resistance to carbon deposition and subsequent deactivation compared to Ni or another transition-metal catalyst. However, its high cost can be stay as an obstacle for the industrial application unless it is introduced with other cheap transition metals. This review emphasizes some salient features of the rational designs and fundamentals for engineering of Pt shape/composition to understand the elementary steps involved in DRM and to exploit the effect of Pt with other noble and earth-abundant-metals to form highly active and stable bi- and tri-metallic catalysts in the context of promoting DRM and their related mechanism, and deactivation regimes supported with several paradigms for rich-hydrogen production. The current critical scientific issues of methane reforming and their challenges, besides the potential prospects, are finally highlighted.