Stability In Dry Reforming Of Methane Research Articles

Synergistic Ni-Ce-SSZ-13 catalysts for enhanced dry reforming of methane

The dry reforming of methane (DRM) serves as a pivotal reaction for hydrogen generation and the simultaneous conversion of methane and carbon dioxide, two major greenhouse gases, into syngas that can further be converted into high-value fuels and chemicals. However, catalyst deactivation imposes a major challenge that prohibits the market penetration of DRM. Here we reported a series of bifunctional Ni-Ce catalysts supported on SSZ-13 (Ni-Ce-SSZ-13) and discovered that a small amount of Ce could significantly enhance the activity, selectivity, and stability for DRM. Optimal ratio of Ni to Ce has been identified to yield peak catalytic performance. The optimal performance is correlated with the maximum Ce3+/Ce4+ ratio as revealed by XPS analysis, which implies an increased presence of oxygen vacancies in the catalysts. It played a crucial role in facilitating the oxidation of activated CH4 species at Ni sites, thereby enhancing DRM activity and diminishing the detrimental coke formation. It is also disclosed that integrating proper amount of Ce fosters its interactions with Ni, effectively preventing the agglomeration of Ni sites. This work presents great implications for the rational design and catalytic synergy of bi-/multi-functional zeolite catalysts for other technological applications.

Dry Reforming of Methane over Pyrochlore-Type La2Ce2O7-Supported Ni Catalyst: Effect of Particle Size of Support.

The properties of supports (such as oxygen vacancies, oxygen species properties, etc.) significantly impact the anti-carbon ability due to their promotional effect on the activation of CO2 in dry reforming of methane (DRM). Herein, pyrochlore-type La2Ce2O7 compounds prepared using co-precipitation (CP), glycine nitrate combustion (GNC) and sol-gel (S-G) methods, which have highly thermal stability and unique oxygen mobility, are applied as supports to prepare Ni-based catalysts for DRM. The effect of the calcining temperature (500, 600 and 700 °C) on La2Ce2O7(CP) has also been investigated. Based on multi-technique characterizations, it is found that the synthesis method and calcination temperature can influence the particle size of the La2Ce2O7 support. Changes in particle size strongly modulate the pore volume, specific surface area and numbers of surface oxygen vacancies of the La2Ce2O7 support. As a result, the distribution of supported Ni components is affected due to the different metal-support interaction, thereby altering the activity of the catalysts for cracking CH4. Moreover, the supports' abilities to adsorb and activate CO2 are also adjusted accordingly, accelerating the removal of the carbon deposited on the catalysts. Finally, La2Ce2O7(CP 600) with an appropriate particle size exhibits the best catalytic activity and stability in DRM.

Synergistic effect of macroporosity and crystallinity on catalyst deactivation behavior over macroporous Ni/CexZr1-xO2–Al2O3 for dry reforming of methane

Dry reforming of methane (DRM) is an outstanding process for transforming methane and carbon dioxide into synthesis gases (H2 and CO). In this study, a special geometrical modification on Ni/CexZr1-xO2–Al2O3 catalyst was applied by introducing a macroporous structure into the support to accelerate the metal support interaction that optimized the distribution of the active sites over the catalyst. Furthermore, we investigated a synergistic effect of the macroporosity and CexZr1-xO2 (CZ) crystallinity over the Ni/CexZr1-xO2–Al2O3 catalyst on its catalytic performance in DRM. Macroporous Ni/CexZr1-xO2–Al2O3 catalysts were prepared via washing (Ni-MaCZA-W) and hydrothermal (Ni-MaCZA-H) methods. Non-macroporous Ni-CZA-H with crystalline CZ was prepared for comparison. The crystalline CZ over macroporous Ni-MaCZA-H had a strong interaction with Ni due to easy accessibility of Ni species to CZ in the macroporous support, resulting in highly dispersed Ni nanoparticles and abundant oxygen vacancies. The unique properties of Ni-MaCZA-H increased catalytic activity and stability in DRM, suppressing coke formation via efficient coke gasification. The Ni species and amorphous CZ over Ni-MaCZA-W resulted in a bimodal Ni size distribution and fast catalyst deactivation. However, even though the crystalline CZ over Ni-CZA-H generated a unimodal distribution of Ni nanoparticles, the non-macroporous Ni-CZA-H resulted in gradual deactivation in the catalytic activity and the production of a different type of coke.

Engineering the Interface and Interaction Structure on Highly Coke-Resistant Ni/CeO2-Al2O3 Catalyst for Dry Reforming of Methane

Designing and tailoring metal-support interaction in Ni-based catalysts with plentiful interfacial sites is of significant interest for achieving a targeted catalytic performance in dry reforming of methane (DRM), but remains as a challenging task. In this work, Ni/Al2O3 and Ni/CeO2-Al2O3 catalysts with the same strong metal-support interaction (SMSI) but distinct interface structure are developed by an improved evaporation-induced self-assembly method using pseudobohemite gel as aluminum source. Ni/CeO2-Al2O3 exhibits superior catalytic activity and stability in DRM in comparison with Ni/Al2O3. The highest CH4 and CO2 conversion reaches at 71.4% and 82.1% for Ni/CeO2-Al2O3, which are higher than that of 64.3% and 75.6% for Ni/Al2O3 at 700 °C. The SMSI effect in Ni/CeO2-Al2O3 provides more active interfacial sites with less coke deposition, and promotes the generation of active formate species which are the key intermediates for DRM. The findings of the present work could possibly pave the way for fabricating catalysts with SMSI strategy for efficient heterogeneous catalysis.

Nickel silicate beta zeolite prepared by interzeolite transformation: A highly active and stable catalyst for dry reforming of methane

• Hydrothermal interzeolite transformation of nickel silicate MWW to *BEA zeolite. • Novel synthesis of nickel silicate beta zeolite using bottom-up method. • In-situ formation of highly dispersed metallic nickel clusters in Ni-BEA. • Highly active and stable Ni catalyst for dry reforming of methane. • Platform technique for the preparation of zeolite-metal composite. The preparation of porous nickel silicates has received considerable attention because of its potential as a catalyst for various applications, such as dry reforming of methane (DRM), CO 2 hydrogenation, and water–gas shift. In this study, we first synthesize the nickel silicate *BEA-type zeolite (Ni-BEA) via the interzeolite transformation of nickel silicate MWW within 12 h. The presence of Ni in the tetrahedral framework of the *BEA structure is experimentally demonstrated using diverse analytical methods. The extraction of framework Ni at high temperatures generates uniform metallic Ni clusters within the pores of the *BEA structure. Ni-BEA exhibits the highest conversions of CH 4 and CO 2 and stability for DRM among the employed catalysts owing to the significant quantity of highly dispersed Ni clusters in the three-dimensional large-pore system. The synthesis of metallosilicate *BEA by interzeolite transformation and in-situ generation of uniform metal clusters can be expanded to the other metal-zeolite catalysts.

Defect-induced formation of nickel silicates on two-dimensional MWW-type catalysts promoting catalytic activity for dry reforming of methane

The surface properties of a catalyst support not only influence the chemical states of the impregnated metals, but also the catalytic performance. Here, we systematically investigated the role of support morphology and defect concentration on the catalytic activity for dry reforming of methane (DRM) by comparing three-dimensional (3D) and two-dimensional (2D) aluminosilicate, borosilicate, and deboronated MCM tWenty-tWo (MWW)-type catalysts. Changes in the surface properties by delamination and/or deboronation as well as their influence on the formation of nickel silicates were experimentally demonstrated. Density functional theory (DFT) calculations were also performed to estimate the stabilization of metallic Ni clusters by the introduction of silanol defect sites on the MWW-type support. The delaminated–deboronated 2D MWW-type catalyst with the highest concentration of nickel silicates, and accordingly, the highest amount of silanol defect sites exhibited remarkable CH4 and CO2 conversions as well as stability for DRM. Unlike conventional Ni/γ-Al2O3, the Ni species in nickel silicate 2D MWW-type catalysts were readily reduced to metallic Ni even without pre-reduction by H2, which is advantageous for practical applications.

Significant Effect of Rh on the h-BN-Supported Ni Catalyst for Dry Reformation of CH4: Insights from Density Functional Theory and Microkinetic Analysis

The design of a catalyst by managing catalytic sites on an atomic scale is significant for tuning catalytic performance and offering high activity and selectivity for dry reforming of methane (DRM). We report a synergy effect of two sets of active sites (Ni and Rh) anchored on the surface hexagonal boron anitride nanosheets(h-BN), the whole reaction mechanism of DRM, as well as the competition processes over h-BN sheet-supported Ni-Rh catalysts (labeled as Ni9/h-BN and Ni8Rh1/h-BN) were studied by density functional theory calculations and microkinetic model analysis in the present work. Our present results show that the stability of hydrocarbon species like CHx(x = 1–4) on the Ni8Rh1/h-BN is significantly lower than that of Ni9/h-BN because of less electron transfer, and thus, strong carbon deposition resistance would be expected after the addition of Rh from the perspective of thermodynamics. CO2 activation is more efficient than that of CH4, and both CH4 and CO2 activation on Ni8Rh1/h-BN is more facile than that of pure Ni9/h-BN, and thus, higher catalytic activity of DRM can be expected on Ni8Rh1/h-BN. CO2 tends to decompose directly on both surfaces, and it was also found that O* is the main oxidizing agent for CH* intermediates and through the CH–O oxidation mechanism. Compared with the Ni9/h-BN surface, the selectivity of the DRM reaction is better on the Ni8Rh1/h-BN surface, and the ratio of H2/CO is close to one on the Ni8Rh1/h-BN surface based on the microkinetic model analysis. The microkinetic model result also shows that coke is difficult to form on the surface of Ni8Rh1/h-BN under experimental conditions. These synergistic effects of the two sets of atom sites on the same surface demonstrated a new method for designing a catalyst with high selectivity and stability for DRM.

Confined high dispersion of Ni nanoparticles derived from nickel phyllosilicate structure in silicalite-2 shell for dry reforming of methane with enhanced performance

Novel structure catalyst of [email protected] with Ni nanoparticles highly dispersed in silicalite-2 zeolite (S2) was designed and synthesized via novel two-steps methods, micro-emulsion method followed by solvent-free crystallization route. Due to the unique two-step synthetic process, the confinement effect of the silicalite-2 shell and stronger metal-support interaction caused by the formation of Ni phyllosilicate intermediate in shell, were regarded as the main reasons for the superb catalytic performances of [email protected] for dry reforming of methane (DRM). Compared with Ni–SiO2 by micro-emulsion method, Ni/S2 by impregnation method and [email protected]–O by direct crystallization, [email protected] catalyst exhibited optimal catalytic activity and stability for DRM. No activity loss was observed during 70 h at high GHSV of 240000 mL g−1h−1. Meanwhile, over spent [email protected] catalyst, hardly any coke was found after the prolonged test, which indicated the remarkable anti-coking ability of [email protected]

Dry Reforming of Methane over Ni–Al2O3 and Ni–SiO2 Catalysts: Role of Preparation Methods

The production of synthesis gas via the conversion of the two greenhouse gases CO2 and CH4 is an efficient process due to its dual industrial and environmental interest. The catalysts based on Ni–SiO2 and Ni–Al2O3 are typical and suitable for this reaction due to their mechanical strength, their good chemical and thermal stability in addition to their low cost and good availability. In this work, we have compared the catalytic performances of these two types of catalysts prepared by two different synthesis methods in dry reforming of methane (DRM).The results indicate that the catalytic performances are much more dependent on the support properties and that they are deeply influenced by the catalyst synthesis method. The textural properties as shown by N2-physisorption analysis are strongly dependent on the support nature in the case of the catalysts prepared by the microemulsion (ME) method and the alumina-based Ni catalyst has a higher specific surface area and a higher pore volume compared to the SiO2 based one. The XRD, H2-TPR and XPS results indicate that the preparation method has a significant influence on the state of NiO species. A Ni particle in the two Ni–SiO2–ME and Ni–Al2O3–ME catalysts prepared by microemulsion is much smaller. The strong metal support interaction promotes the formation of NiAl2O4 and Ni2SiO4 species respectively during the catalyst preparation process and makes the reduction of corresponding catalysts very difficult which may lead to a decrease in the content of active Ni species and give the Ni–Al2O3–ME catalyst a relatively low catalytic activity in DRM, especially when it is reduced under unfavorable conditions as is the case in this work. However, the strong metal support interaction between Ni and the support is also of beneficial to the formation and stabilization of small Ni particles well dispersed on the support after reduction of the Ni–SiO2–ME catalyst. In this system, the sintering and the carbon deposition are inhibited and the catalyst presents both better activity and stability. The Ni/Al2O3 catalyst exhibits a synergistic effect between the various phases NiO and NiAl2O4 formed during the synthesis process due to the different interactions strength between metal and support, which are in favor of the dispersion and stabilization of NiO species. As a result, Ni/Al2O3 provided with both proper textural properties and this synergistic effect, exhibits superior catalytic performances in term of activity, selectivity and stability in DRM. Despite the formation of carbon over this catalyst, it maintains its stability during a long-term test of more than 66 hours. This is due to the formation of active type of carbon and the delocalization of the Ni active sites on the latter to maintain their activity.

Intermetallides as the catalysts for carbon dioxide reforming of methane

Intermetallic catalysts for dry reforming of methane (DRM) based on Ni3Al with low content of Pt and Ru have been developed. Self-propagating high-temperature synthesis (SHS) was used as a method of catalyst synthesis. Ion implantation was used to change the physical, chemical and catalytic properties of Ni3Al as a matrix for this new type of catalysts for DRM. Ions of Pt and Ru were accelerated in an electrical field and impacted into a solid Ni3Al. The catalytic performances were evaluated between 600°C and 900°C at atmospheric pressure. The feed was CH4/CO2/He=20/20/60vol.% mixture. Particle size and chemical evolution of catalysts were studied by XRD (in situ and ex situ), SEM, EDS, HRTEM+EDS and XPS. The active components were shown to be primarily dispersed in the nearsurface layer of Ni3Al support as nanoparticles of size 5–10nm, which were distributed homogeneously or heterogeneously, depending on the catalyst composition. Spinel structure of some catalysts is resistant to carbonization and provides high catalyst stability in DRM. Modification of catalyst by ion implantation had several positive impacts: 1) high catalytic activity and stability in DRM, 2) reducing of carbon deposits, 3) Pt and Ru prevent Ni phase sintering by avoiding particle coalescence.

Modulating morphology and textural properties of ZrO2 for supported Ni catalysts toward dry reforming of methane

This work presents a facile and efficient approach to modulate morphology and textural properties of ZrO2 through ammonium fluoride‐urea assisted hydrothermal (FUAH) method with diverse parameters including molar ratio of NH4F to zirconium (nf/z), molar ratio of urea to zirconium (nu/z), hydrothermal temperature (Thydroth), and hydrothermal time (thydroth), which serve as support for supported Ni catalysts toward dry reforming of methane (DRM) to produce synthesis gas. The plausible mechanism for forming ZrO2 supports with different morphologies under diverse hydrothermal conditions was proposed. Various characterization techniques were employed to investigate the effect of preparation parameters on the morphology and textural properties of the as‐synthesized ZrO2 supports, as well as to reveal the structure‐performance relationship of the Ni/ZrO2 catalysts prepared by L‐arginine assisted incipient wetness impregnation method toward DRM reaction. The developed supported Ni catalyst on hierarchically structured ZrO2 with pinecone shape prepared by FUAH method (Ni/ZrO2‐FUAH) demonstrates higher activity and stability for DRM than that on ZrO2 prepared by traditional hydrothermal method (Ni/ZrO2‐H). The higher activity of Ni/ZrO2‐FUAH than Ni/ZrO2‐H can be ascribed to the higher Ni dispersion, smaller Ni crystalline size, and enhanced reducibility of NiO, significantly affected by morphology of support, as well as the higher coke‐resistance catalytic stability can be ascribed to smaller Ni particle size and stronger Ni‐support interaction, strongly dependent on morphology and textural properties of ZrO2 supports that affected by FUAH process parameters. The outstanding catalytic performance of the developed Ni/ZrO2‐FUAH catalyst allows it to be a promising candidate for synthesis gas production through DRM reaction. © 2017 American Institute of Chemical Engineers AIChE J, 63: 2900–2915, 2017