Coke Deposition Research Articles

OXIDATIVE REGENERATION OF METAL COMPLEX CATALYTIC SYSTEM

When carrying out thermocatalytic destruction of hydrocarbon feedstock, catalysts are deactivated due to the formation of surface coke, which blocks active centers. In order to restore their previous activity and selectivity, as well as extend their service life, a process of catalyst regeneration is carried out. One of the effective methods for restoring the original activity of deactivated catalysts is oxidative regeneration, which is based on the oxidation of coke deposits on the surface of the catalyst. The article examines the dependences of the formation of surface coke when varying the temperature regime of the process from 450 °C to 550 °C during the thermocatalytic destruction of heavy petroleum feedstock – West Siberian oil fuel oil in the presence of a new metal complex catalytic system, where the active component is a chloroferrate complex (NaFeCl4 or TCFN) in an amount 10 %, deposited on a carrier, which is a deeply decationized Ymmm zeolite of the acidic form (H-form). The patterns of oxidative regeneration of a metal-complex catalytic system were studied by distilling off highly volatile products in a flow of inert gas (helium) and oxygen-containing gas. During the experiments, it was found that with an increase in the temperature of the thermocatalytic destruction process from 450 °C to 550 °C, a slight increase in coarse deposits on the surface of the catalyst was observed from 2,6 % wt. up to 3,5 % wt. respectively. When carrying out the process of oxidative regeneration of a carbonized catalyst with air oxygen (in a flow of helium) at a temperature of 500 °C for 60 min only volatile components are initially removed, and further calcination takes up to 180 min allows for complete burning of surface coke.

Steam cracking of sulfur containing compounds: A fundamental modelling study

Sulfur-containing additives are commonly used in industrial steam cracking to mitigate carbon monoxide (CO) formation. Their impact on solid coke deposition in reactors is well-studied but not fully understood. This study investigates the decomposition of five common sulfur compounds (DMDS, DMS, DMSO, CS2, COS) in both inert and hydrocarbon environments within the steam cracking industry. To achieve this, an in-house automated network generation tool called Genesys and a validated ab initio methodology at the CBS-QB3 level are used. This combination generates a comprehensive kinetic model with precise thermodynamic and kinetic parameters. The kinetic model is rigorously validated against experimental data from prior studies under various conditions, including inert nitrogen atmospheres and hydrocarbon matrices (using ethane and heptane). Experimental setups involve bench-scale annular quartz reactors and pilot-scale stainless steel reactors. Remarkably, the kinetic model accurately predicts primary products and captures secondary product trends across diverse conditions without parameter adjustments. Rate of production analyses reveal critical decomposition pathways during sulfur-containing additive pyrolysis and the influence of hydrocarbon matrices. Notably, these additives primarily yield H2S upon decomposition, with CS2, SO2 and thiophene as minor products. In conclusion, the developed fundamental kinetic model accurately predicts product formation during the pyrolysis of DMS, DMDS, DMSO, CS2 and COS, whether in nitrogen or a hydrocarbon matrix, without altering core thermodynamic and kinetic parameters.

Local coordination environment triggers key Ni-O-Si copolymerization on silicalite-2 for dry reforming of methane

The development of dry reforming of methane (DRM) catalysts with good Ni loading, while retaining high metal dispersion is a critical issue, given the harsh industrial-relevant conditions. Here, we demonstrate the impact of the local coordination environment on the DRM activity of Ni-silicalite-2 (Ni-S2) catalysts. The grafted Ni(II) intermediates with high Ni-O-Si copolymerization (coordination number ratio Si: Ni=2.28) are discovered to redisperse Ni sites, even at 10 wt% Ni loading. Then, the partial S2 recrystallizes into new SiO2-nanowires to anchor Ni nanoparticles, via an ethylenediamine-assisted dissolution-recrystallization (enDR). Compared to the typical Ni-S2 catalyst with Ni phyllosilicate (CN ratio Si: Ni＜1), the Ni-S2-enDR shows high dispersion and stability at 800 °C and 450 L gcat−1 h−1, exhibiting negligible coke deposition and no growth of 4.25 nm Ni nanoparticles. The atomic level insights in nickel and silicon coordination reported in this work provide an instructive way of designing stable DRM catalysts.

The structure of deposited coke on hydrocracking and reforming catalysts: Coke deactivation and kinetics

AbstractThis comprehensive study investigates the structural deposition of coke, particularly its association with sulphides, in spent hydrocracking and reforming catalysts, leveraging advanced kinetic modelling and characterization techniques. Its objective is to elucidate coke removal kinetics, offering insights into optimizing catalyst regeneration. Utilizing thermogravimetric analysis, spectroscopic methods, and modelling, the research outlines the characteristics and kinetic behaviour of coke during regeneration. The novelty aspect of this study is the use of a reaction‐based model for accurate kinetic analysis and identifying optimal conditions for coke removal. The study recognized both hydrogen‐deficient and hydrogen‐rich amorphous coke, alongside graphitic coke spent catalysts. Thermogravimetric analysis revealed that coke constitutes ~23.8% and 4.6% of the total weight in hydrocracking and reforming catalysts, respectively. The traditional model‐free method for deactivation was found inadequate in predicting coke in the spent reforming catalyst, likely due to the presence of low‐temperature hydrocarbons of soft coke within the catalyst pores. In contrast, a reaction model‐based deactivation approach yielded more consistent evaluations for soft and hard coke of spent catalyst. For the spent hydrocracking catalyst, the estimated activation energies for coke decomposition were 41.56 and 128.97 kJ/mol for soft and hard coke, respectively, during regeneration. Although the coke in the spent reforming catalyst displayed similar temperature trends for decomposition, the average activation energies were 52.61 and 128.62 kJ/mol for soft and hard coke, respectively. The theoretical results from the multi‐reaction model for coke decomposition are consistent with the experimental results for both catalysts.

Comparative investigation of low temperature oxidized and pyrolyzed cokes from the inferior heavy oil: Structural feather, thermo-oxidation behavior, and kinetics

It was crucial to study the low temperature coking process for the heavy oil, which affected the fuel availability and subsequent in-situ combustion progress. From this perspective, low temperature coking experiments with different atmospheres were accomplished for the inferior heavy oil to obtain oxidized (cokeLTO) and pyrolytic (cokeLTP) cokes, which were further employed to trace structural feathers via joint analysis of elemental analysis, Fourier transform infrared spectrophotometry (FTIR) and X-ray photoelectron spectroscopy (XPS) spectra, and to characterize thermo-oxidative characteristics and kinetics via different thermal analyses (TG-DTG/DSC) and model-free methods. The results showed that a relatively less aliphatic and more aromatic structures were contained in cokeLTO with a relatively higher proportion of C-O, C = O, O-C = O groups and C/H ratio, implying that oxygen atom was served as the promoter to replace hydrogen atom and accelerate macromolecular structure formation. While the decomposition and conversion of N- and S- functional groups were complicated and insensitive to the coking atmosphere. Furthermore, cokeLTO had a more dominant thermo-oxidation behavior than cokeLTP with better exothermic characteristic and lower activation energy distribution. From this study, it could provide a vital piece of updated insights on the role of low temperature oxidation process in coke deposition and feature.

Catalytic Supercritical Water Gasification of Canola Straw with Promoted and Supported Nickel-Based Catalysts.

Lignocellulosic biomass such as canola straw is produced as low-value residue from the canola processing industry. Its high cellulose and hemicellulose content makes it a suitable candidate for the production of hydrogen via supercritical water gasification. However, supercritical water gasification of lignocellulosic biomass such as canola straw suffers from low hydrogen yield, hydrogen selectivity, and conversion efficiencies. Cost-effective and sustainable catalysts with high catalytic activity for supercritical water gasification are increasingly becoming a focal point of interest. In this research study, novel wet-impregnated nickel-based catalysts supported on carbon-negative hydrochar obtained from hydrothermal liquefaction (HTL-HC) and hydrothermal carbonization (HTC-HC) of canola straw, along with other nickel-supported catalysts such as Ni/Al2O3, Ni/ZrO2, Ni/CNT, and Ni/AC, were synthesized for gasification of canola straw on previously optimized reaction conditions of 500 °C, 60 min, 10 wt%, and 23-25 MPa. The order of hydrogen yield for the six supports was (10.5 mmol/g) Ni/ZrO2 > (9.9 mmol/g) Ni/Al2O3 > (9.1 mmol/g) Ni/HTL-HC > (8.8 mmol/g) Ni/HTC-HC > (7.7 mmol/g) Ni/AC > (6.8 mmol/g) Ni/CNT, compared to 8.1 mmol/g for the non-catalytic run. The most suitable Ni/ZrO2 catalyst was further modified using promotors such as K, Zn, and Ce, and the performance of the promoted Ni/ZrO2 catalysts was evaluated. Ni-Ce/ZrO2 showed the highest hydrogen yield of 12.9 mmol/g, followed by 12.0 mmol/g for Ni-Zn/ZrO2 and 11.6 mmol/g for Ni-K/ZrO2. The most suitable Ni-Ce/ZrO2 catalysts also demonstrated high stability over their repeated use. The superior performance of the Ni-Ce/ZrO2 was due to its high nickel dispersion, resilience to sintering, high thermal stability, and oxygen storage capabilities to minimize coke deposition.

The insight into reaction mechanism of diethylamine catalytic abatement over various Cu-based catalysts

This work investigated the reaction behaviors of diethylamine (DEA) catalytic oxidation on various Cu-based catalysts with different supports (TiO2, HZSM-5(27), HZSM-5(130) and S-1). It was found that the acidic environment of catalysts greatly influenced reaction pathways of DEA oxidation. On Cu5/TiO2 catalyst mainly with Lewis acidity, DEA preferentially dissociated through a two-step dehydrogenation to produce acetonitrile and ethylene, while on Cu5/HZSM-5(27) catalyst with strong Brønsted acidity, DEA could directly decompose into ethylamine and ethylene via N-C cleavage. Both pathways existed simultaneously over Cu5/HZSM-5(130) with decreased Brønsted acidity. Thereafter, acetonitrile could be further oxidized on the Cu5/TiO2 catalyst to generate a large amount of NOx via NCO(a) intermediates over-oxidation, while ethylamine on Cu5/HZSM-5 samples would convert to acetamide and then produced N2 and CO2. The Cu2+ species due to enriched Brønsted acid sites in Cu5/HZSM-5 catalysts ensured excellent N2 selectivity via internal SCR mechanism. Additionally, the strong Brønsted acidity of Cu5/HZSM-5(27) could induce the polymerization of carbonaceous intermediates and thereby resulted in severe coke deposition. As for Cu5/HZSM-5(130) and Cu5/S-1 with relatively lower Brønsted acidity and reducibility would release some unwanted gas-phase by-products like ethyl-isocyanate. This work provided useful guidance for designing NVOCs catalysts with high activity and less toxic by-products.

5Ni/MgO and 5Ni/MgO + MOx (M = Zr, Ti, Al) Catalyst for Hydrogen Production via Dry Reforming of Methane: Promotor-Free, Cost-Effective, and Handy Catalyst System

Utilization of CO2 as a promising oxidant under dry reforming methane (DRM) can mitigate two greenhouse gases (CO2 and CH4) together, as well as DRM reaction may be a source of H2 energy in future. The cost-effective and handy catalyst preparation procedures like mixing, drying and calcining may turn this reaction from lab to industry. In this line, herein, 5Ni/MgO and 5Ni/MgO + MOx (M = Zr, Ti, Al) catalysts were prepared, investigated for DRM and characterized by X-ray diffraction, Raman, temperature programmed reduction/desorption, thermogravimetry and transmission electron microscope. Among the prepared catalysts, the 5Ni/MgO + TiO2 catalyst exhibits the highest concentration of active Ni sites enhanced reducibility under oxidizing and reducing environments, but catalytic excellency is hindered by severe graphitic-type coke deposition. On the other hand, the 5Ni/MgO + Al2O3 catalyst predominantly comprises metallic Ni resulting from the reduction of “strongly interacted NiO”, expanded surface area and the highest concentration of easily accessible active sites, contributing to its superior performance (H2 yield ~ 71% up to 430 min time on stream) under oxidizing and reducing conditions during DRM. The outstanding performance of the 5Ni/MgO + Al2O3 catalyst marks a significant stride towards the development of an industrially viable, cost-effective, and convenient catalyst system for DRM.Graphical

Effect of calcination temperature on Co/sepiolite catalyst for hydrogen production by ethanol steam reforming: Co speciation from phyllosilicate to spinel

Hydrogen production via ethanol steam reforming (ESR) was conducted over amorphous sepiolite (SEP) supported Co based catalysts, deeming as a green and sustainable strategy for renewable energy. However, the subtle regulation to the ESR reactivity of Co/SEP catalysts still remains a challenge. Given the structure sensitive property of ESR, calcination temperature, as a vital regulation parameter, was used to control the key physicochemical properties of catalysts. By various characterization techniques, the results revealed that a calcination temperature mediated metal-support interaction was manifested in the form of Co speciation evolution. With increasing calcination temperature, the occurrence states of Co species change from Co oxides to Co-phyllosilicate then to Co-Al spinel. The ESR experiments indicated that Co/SEP-600 catalyst possessed a suboptimal activity via a dehydrogenation route and a 50 h stability due to a compromising among Co-phyllosilicate dominated MSI, texture, Co0 nanoparticle size and acid-base property. The further improvement of calcination temperature only brought about a poor stability of Co/SEP-700 with a phase transformation or a low activity of Co/SEP-800 with an irreducible Co-Al spinel. Hence, the interaction type of Co with SEP framework Si/Al atoms determined the ESR reactivity of the catalysts, which was modulated by the calcination temperature. Additionally, abundant graphitic coke deposition on the agglomerated Co0 grains was attributed the weak MSI, such as Co/SEP-400, while a slight coke deposition appeared at Co/SEP-800 with an irreducible Co-Al spinel phase.

Enhancing catalytic performance, coke resistance, and stability with strontium-promoted Ni/WO3-ZrO2 catalysts for methane dry reforming

The first step of the DRM reaction is just the decomposition of CH4 into CH4−x (x = 1–4). The next step comprises two steps, namely the oxidation of CH4−x into syngas (by CO2) and the self-polymerization of CH4−x species. The earlier one is known as dry reforming of methane (DRM), and the latter one generates carbon deposits over the catalyst surface. In this study, we investigated the impact of 1–3 wt% Sr over Ni-based catalysts on a ZrO2-WO3 support on the catalytic activity and coke deposit. Various characterization techniques such as thermogravimetric analysis, X-ray diffraction, Raman spectroscopy, temperature-programed oxidation, temperature-programed reduction, and temperature-programed desorption were used to assess the physicochemical properties of the fresh and spent catalysts. The addition of 2wt% Sr promoter significantly improves the catalyst’s basicity in strong basic sites region through Sr2+ mediated interaction of CO2 species as well as inhibits the deposition of carbyne type carbon. Enhanced CO2 interaction results into the potential oxidation of carbon deposit and the highest CH4 conversion, reaching 60% up to 470 min TOS at a reaction temperature of 700 ℃.Graphical abstract

Cost-Effective Single-Step Synthesis of Metal Oxide-Supported Ni Catalyst for H2-Production Through Dry Reforming of Methane

AbstractPreparing catalysts from cheap metal precursors in a single pot are an appealing method for reducing catalytic preparation costs, minimizing chemical waste, and saving time. With regards to the catalytic conversion of dry reforming of methane, it offers the prospect of significantly reducing the cost of H2 production. Herein, NiO-stabilized metal oxides like Ni/TiO2, Ni/MgO, Ni/ZrO2, and Ni/Al2O3 are prepared at two different calcination temperatures (600 °C and 800 °C). Catalysts are characterized by X-ray diffraction, Raman spectroscopy, surface area-porosity analysis, Temperature program experiments, infrared spectroscopy, and thermogravimetry analysis. The MgO-supported Ni catalyst (Ni/MgO-600), ZrO2-supported Ni catalyst (Ni/ZrO2-600), and Al2O3-supported Ni (Ni/Al2O3-600) catalyst calcined at 600 °C show initial equal H2 yields (~ 55%). The population of CH4 decomposition sites over ZrO2-supported Ni catalyst remains highest, but H2-yield drops to 45% against high coke deposition. The catalytic activity remains constant over the Ni/MgO-600 catalyst due to the enrichment of “surface interacted CO2-species”. MgO-supported Ni catalyst calcined at 800 °C undergoes weak interactions of NiO-M′ (M′ = support), serious loss of CH4 decomposition sites and potential consumption of H2 by reverse water gas shift reaction, resulting in inferior H2 yield. H2-yield remains unaffected over an Al2O3-supported Ni catalyst even against the highest coke deposition due to the formation of stable Ni (which exsolves from NiAl2O4) and proper matching between carbon formation and rate of carbon diffusion.

The effect of hierarchical pore structure SAPO-34 catalyst on the diffusion and reaction behavior in MTO reaction

Establishing the hierarchical pore structure is considered as a feasible approach for enhancing diffusion and improve catalytic efficiency of SAPO-34 zeolite in the methanol-to-olefin process. Nevertheless, under reaction conditions, the correlation among the diffusion behavior in the crystal, coke deposition behavior and catalytic performance of SAPO-34 catalysts with varying pore structures remains to be clarified. Herein, we revealed the structure–activity relationship between the hierarchical pore structure, the catalytic performance and the anti-coke deposition performance of the catalyst in the MTO reaction via the synergy of reaction–diffusion experiments and molecular simulation, then the mechanism of the hierarchical pore SAPO-34 catalyst to eliminate the diffusion limit and improve the accessibility of acid sites was clarified. The results demonstrated that the establishment of a hierarchical pore structure strengthened the diffusion of reactant methanol in the pores, leading to the diffusion resistance being reduced by 5 times and the diffusion coefficient being improved by two orders of magnitude. The key reaction rate-determining step shifted from micropores diffusion to the adsorption of acid sites in hierarchical pores, and the catalytic efficiency of the catalyst was increased by 3 times. Furthermore, with the establishing hierarchical pore technique, the expansion of the accommodation space for coke deposition led to a reduction in the blocking of pores due to coke deposition, particularly around the orifices. Moreover, the accessibility of the reactant molecules to the acid sites within the pores was enhanced, resulting in a balanced ratio between pore blockage and acid site coverage, thereby improving the anti-coke deposition performance of the SAPO-34 catalyst. This work can provide important foundational data and theoretical guidance for the study of reaction–diffusion synergistic interaction in zeolite catalysis reactions.

Coke Formation and Zeolite Catalyst Effects on Products from Co‐pyrolysis of Waste Tyre and Poplar Wood in a Semi‐Batch Reactor under N2 Atmosphere

Herein, it is aimed to investigate the effect of zeolite catalyst on the co‐pyrolysis process of waste tyre and poplar wood. A laboratory‐sized reactor is used to pyrolyze 15 g of sample at 500 °C under atmospheric pressure. In the results, it is indicated that co‐pyrolysis affects the properties of the products. Comparing to single feedstock, the co‐pyrolysis enhances the yields of bio‐oil, while reducing the formation of char. The pyrolysis of poplar wood produces 23.3 wt% of bio‐oil, while the pyrolysis of tyre yields 25 wt% of bio‐oil. However, it is 31.29 wt% for the co‐pyrolysis process. Higher content of valuable compounds are formed in the bio‐oil, which improve the fuel properties of the bio‐oil. The zeolite catalyst alters the characteristics of the products obtained from the co‐pyrolysis process. The gaseous products show a decrease in the concentrations of carbon monoxide and carbon dioxide when the catalyst is present. The liquid product analysis reveals the presence of light aromatics such as ethyl benzene and light linear compounds such as alkanes including octane, hexane, etc. The analysis of the catalysts suggests that a very small amount of coke deposits on the catalyst due to the slight increase in carbon content.

Intermetallic Ni3Ga1 Catalyst for Efficient Ammonia Reforming of Light Alkane.

Ammonia reforming of light alkane is conventionally employed for HCN production where coproduct H2 is burned for heating owing to the high reaction temperature (1200 °C) of such a highly endothermic process. Here, we show that a Ni3Ga1 intermetallic compound (IMC) catalyst is highly efficient for such a reaction, realizing efficient conversion of C1-C3 alkanes at 575-750 °C. This makes it feasible for on-purpose COx-free H2 production assuming that ammonia, as an H2 carrier, is ubiquitously available from renewable energy. At 650 °C and an alkane/ammonia ratio of 1/2, ethane and propane conversion of ∼20% and methane conversion of 13% were obtained (with nearly 100% HCN selectivity for methane and ethane) over the unsupported Ni3Ga1 IMC, which also shows high stability due to the absence of coke deposition. This breakthrough is achieved by employing a stoichiometric Ni3Ga1 mixed oxalate solid solution as the precursor for the Ni3Ga1 IMC.

Relationship between hydrogenation degree and pyrolysis performance of jet fuel

Relationship between hydrogenation degree and pyrolysis performance of jet fuel

Efficient and stable Fe-Ce-Al catalyst for catalytic deoxygenation of lignin for phenol and hydrocarbon-rich fuel: Effect of the synthesis method

To develop a structure-tailoring catalyst for catalytic conversion of lignin for value-added chemicals, a series of novel Fe-Ce-Al metal oxide catalysts was synthesized via different methods to tailor activity and structure for catalytic pyrolysis of lignin to enhance hydrocarbon-rich bio-oil. The results revealed that FeCeAl-CO catalysts derived from coprecipitation method with smaller particle sizes exhibited excellent catalytic deoxygenation activity due to higher Lewis/Brønsted acid, reversible Ce3+/Ce4+ redox pairs, tailorable oxygen vacancies and promoted β-O-4, aromatic-OCH3 and side-chain cleavage. Additionally, coprecipitation method was facilitated to enhance hydrogen transfer, side-chain cleavage and aromatization reactions, while wet impregnation was beneficial to enhance demethoxylation and H-abstraction activity. During catalytic pyrolysis process, over 57.91% of hydrocarbon, including 20.21% and 25.71% for aromatics and olefins were achieved over FeCeAl-CO catalyst. Over 60.74% phenols and 52.48% alkylphenols were obtained over Fe-Ce/Al2O3-IM catalyst due to synergistic effect of FeOx and CeOx species. Fe-Ce-Al catalyst exhibited great activity and stability after fourth run, greater Brønsted acid-favored lignin cleavage and coke deposition, and metal active species leaching, oxidation and pore blockage were the key reasons for deactivation. Therefore, these findings could provide a cost-effective method for designing structure-tailoring catalysts for direct catalytic deoxygenation of lignin to generate hydrocarbon-rich upgrading bio-oil.

Modification effect of cerous nitrate on hierarchical Beta molecular sieves

A simple and facile co-calcination strategy of Beta molecular sieves and cerous nitrate is proposed. Based on the results of XRD, UV–Vis, in-situ FTIR, and 29Si MAS NMR techniques, open-site configurations of Ce(III)O4 and Ce(IV)O4 tetrahedrons are observed due to a large ionic radius of Ce3+ and Ce4+ ions. Open-site configurations result in a low ratio of BrØnsted and Lewis acid sites in HBeta-Ce-6. In the isomerization of α-pinene, a higher amount of Lewis acid sites increases the yield for camphene. BrØnsted acids are accessible for α-pinene to form limonene due to a high surface area and low coke deposition. Isomorphous incorporation of Ce3+ occurs and a decreasing selectivity for limonene are observed using regenerated catalysts. These results indicate that co-calcination strategy protects Beta molecular sieves from thermal destruction, endows Beta molecular sieves with a higher relative crystallinity and porosity during calcination.

General Synthesis of High-Entropy Oxide Nanofibers.

The discovery of high-entropy oxides (HEOs) in 2015 has provided a family of potential solid catalysts, due to their tunable components, abundant defects or lattice distorts, excellent thermal stability (ΔG↓ = ΔH - TΔS↑), and so on. When facing the heterogeneous catalysis by HEOs, the micrometer bulky morphology and low surface areas (e.g., <10 m2 g-1) by traditional synthesis methods obstructed their way. In this work, an electrospinning method to fabricate HEO nanofibers with diameters of 50-100 nm was demonstrated. The key point lay in the formation of one-dimensional filamentous precursors, during which the uniform dispersion of five metal species with disordered configuration would help to crystallize into single-phase HEOs at lower temperatures: inverse spinel (Cr0.2Mn0.2Co0.2Ni0.2Fe0.2)3O4 (400 °C), perovskite La(Mn0.2Cu0.2Co0.2Ni0.2Fe0.2)O3 (500 °C), spinel Ni0.2Mg0.2Cu0.2Mn0.2Co0.2)Al2O4 (550 °C), and cubic Ni0.2Mg0.2Cu0.2Zn0.2Co0.2O (750 °C). As a proof-of-concept, (Ni3MoCoZn)Al12O24 nanofiber exhibited good activity (CH4 Conv. > 96%, CO2 Conv. > 99%, H2/CO ≈ 0.98), long-time stability (>100 h) for the dry reforming of methane (DRM) at 700 °C without coke deposition, better than control samples (Ni3MoCoZn)Al12O24-Coprecipitation-700 (CH4 Conv. < 3%, CO2 Conv. < 7%). The reaction mechanism of DRM was studied by in situ infrared spectroscopy, CO2-TPD, and CO2/CH4-TPSR. This electrospinning method provides a synthetic route for HEO nanofibers for target applications.

Interface engineering of Ce/La-doped hydrochar-supported nickel catalysts for enhanced tar reforming performance at low temperature

Catalytic reforming of biomass tar to syngas-especially under mild temperature-is an attractive albeit elusive route, necessitating the manufacture of highly efficient catalysts, in particular, from inexpensive, sustainable, and renewable resources as a prerequisite. Two interface-engineering strategies, including one-pot hydrothermal carbonization (HTC) approach and two-step HTC-impregnation method, were applied to fabricate a series of Ce/La-doped hydrochar-supported nickel catalysts, employing pinewood sawdust-derived hydrochar as the support, nickel as the active sites, and Ce or La as the promoter species. After the optimization of synthetic variables and operation conditions, the Ni0.1/Ce0.05-HC catalysts prepared by the two-step HTC-impregnation method simultaneously exhibited boosted activity, selectivity and recyclability than the Ni/HC counterpart without Ce addition as well as reported state-of-the-art catalysts in steam reforming of biomass tar at a low temperature of 600 °C. This exceptional catalytic performance was mainly attributed to the modulation of geometric structure and electronic structure of the exposed active sites by appropriate inclusion of cerium on the hydrochar-based nickel catalyst, which favored the water-gas shift, boudouard reaction and coke gasification, thereby imparting the materials with remarkable resistance against metal sintering and coke deposition during the steam reforming process. The result in this work underscores that the controlled interface between Ni species and hydrochar support by addition of Ce, which pertain to the hydrothermal processing technique, is a promising blueprint toward effective fuel production from waste biomass.

Sustainable carbon-based nickel catalysts for the steam reforming of model compounds of pyrolysis liquids

Steam reforming of biomass-derived pyrolysis liquids (bio-oil) to produce hydrogen with carbon-based Ni catalysts is gaining attention due to their advantages in terms of cost, sustainability and activity. However, the catalytic activity at long times on stream is compromised by either coke deposition or gasification of the support. To face these drawbacks, two activated carbons have been studied as Ni catalyst support: a microporous carbon of high purity and a mesoporous carbon with phosphorus surface groups. The activity and long-term stability of these catalysts have been studied for the steam reforming of model compounds of bio-oil. The microporous support provided a slightly higher H2 production and lower contribution of methanation reaction. However, gasification of this support after 20 h led to a decline in the activity, and massive formation of carbon nanotubes and coke. Nevertheless, the resulting material maintained an outstanding stability with high and stable H2/CO ratio for 50 h. The P-containing catalyst showed a remarkable long-term stability, but lower H2/CO ratio. Carbon gasification was less significant in this catalyst due to the presence of surface phosphorus groups, and the generation of nickel phosphides, which hampers the growth of pyrolytic carbon and carbon nanotubes, leading to a superior stability.