Catalyst Sintering Research Articles

Highly dispersed and stable Pt clusters encapsulated within ZSM-5 with aid of sodium ion for partial oxidation of methane

The alkaline ions are usually added to regulate pH and accommodate charge balance during silica-alumina zeolite synthesis. Importantly, alkaline ions play a crucial role in stabilizing metal species encapsulated within silica-alumina zeolite. Pt@ZSM-5 samples with different amounts of sodium ions were synthesized for partial oxidation of methane (POM) reaction. The properties of Pt@ZSM-5 catalyst was characterized by XRD, ICP, TEM, CO-TPR and FT-IR techniques. The presence of alkaline ions promotes the combination of Pt with hydroxyl groups within zeolite and improves stability and dispersity of Pt species further. Appropriate amounts of sodium ions activate platinum and promote the formation of Pt-Ox(OH)yNa species. The experiment results also suggest that the partially oxidized Pt-Ox(OH)yNa specie is the active site of the POM reaction and inhibits sintering of catalyst. This strategy provides a highly active and stable catalyst synthesis method, expanding the application of metal encapsulated within silica-alumina zeolite.

Latest trends in Syngas production employing compound catalysts for methane dry reforming

The rise in the global population has ultimately steered to increase in global energy consumptions. This masqueraded several challenges worldwide. The most troublesome being the accumulation of greenhouse gases (GHGs) that induced a global climatic change. The utilization of fossil fuels like petroleum, coal and natural gas on the copious scale has led to the elevated levels of carbon dioxide (CO2) and methane (CH4) in the global environment. Dry reforming of methane (DRM) is a highly favorable technique as it utilizes two of the prominent GHGs, CH4 and CO2 to generate a useful and valuable product viz. syngas. However, the deactivation, coking and sintering of catalysts are still the main hurdles in the commercialization of the process. The compound metal catalysts have shown enhanced activity and prolonged durability when compared with monometallic catalysts due to enhanced morphology, improved and stable catalytic structure, i.e., both coke and sintering resistant at high temperatures. This brief review spotlights the recent developments in DRM by emphasizing parameters such as the effects of catalyst support, bimetallic catalyst, promoters and strong metal-support interaction (SMSI) in the last decade.

Contemporary trends in composite Ni-based catalysts for CO2 reforming of methane

The emission of greenhouse gases (GHGs), e.g. CO2 and CH4 into the atmosphere leads to an undesirable effect on climate change. One viable solution is to convert these two GHGs into valuable syngas via catalytic dry reforming of methane (DRM). Due to low-cost, feasibility, good catalytic activity, Ni-based catalysts have been used and tested extensively for DRM. However, the main limitation is the catalyst deactivation which occurs due to carbon formation and sintering of catalyst at high temperatures. This review aimed to provide up-to-date summary on the DRM process, including aspects of composite (bimetallic and trimetallic) catalysts and also the influence of doping metal on the catalysts. Furthermore, the metal support studies with the reaction mechanisms and kinetic studies, the latest catalyst configuration and their preparation methods have been highlighted. Therefore, the impending research focuses on composite catalysts and its density functional theory modelling for DRM to design an ideal catalyst.

Hydrogen bromide in syngas: Effects on tar reforming, water gas-shift activities and sintering of Ni-based catalysts

Hydrogen bromide is an emerging impurity of syngas formed during gasification of electronic and municipal solid waste. The influence of HBr on catalytic activity and deactivation of various Ni-based tar reforming catalysts was investigated. The data demonstrate the detrimental effect on catalytic properties (1) occurs at HBr concentrations above 500 ppmv, (2) is more severe compared to HCl and (3) varies greatly with the catalyst structure. The characterization of spent catalysts revealed that the formation of chemisorbed Ni-Br species, enhanced Ni sintering and depletion of NiO-Al2O3 sites could be the reasons for the loss of tar reforming and water-gas shift activities. On the other hand, no significant effect of HBr on catalyst coking was observed. The comparison of different catalysts demonstrated that the negative HBr impact can be successfully mitigated by developing a nanostructured catalyst with high porosity and Ni dispersion that ensure the strong Ni-support interaction.

Revealing the Role of Surface Composition on the Particle Mobility and Coalescence of Carbon-Supported Pt Alloy Fuel Cell Catalysts by In Situ Heating (S)TEM

Thermal annealing is an indispensable process during the preparation and structural ordering of Pt alloy fuel cell catalysts, which exhibit superior electrocatalytic activities as compared to Pt catalysts and thus enable decreased Pt usage. However, thermal annealing usually induces detrimental particle sintering, which greatly offsets the performance enhancement. Although the mechanisms of particle sintering of monometallic Pt catalysts have been well studied, knowledge on the key factors controlling the particle sintering of Pt alloy catalysts is still very poor. Herein, we perform in situ heating (scanning) transmission electron microscopy of carbon-supported low-Pt alloy catalysts (PtFe3, PtCo3, and PtNi3) and reveal that the surface composition plays a key role in both the particle mobility and the coalescence process of the supported low-Pt nanoparticles (NPs) under high temperatures. A surface enrichment of the less-noble transition metals not only induces a faster particle coalescence due to enhanced surface diffusion, but also causes a higher mobility of the NPs on the carbon support due to a strong chemical interaction between the less-noble transition metals and the carbon support. In contrast, the Pt richer surface results in a lower NP mobility as well as slower surface diffusion across contact NPs, which contributes to a higher antisintering capability. Our results suggest that controlling the surface composition, for example, by engineering the elemental growth kinetics during nanoparticle synthesis, is critical for controlling the particle sintering of Pt alloy catalysts during thermal annealing.

Sorption enhanced steam reforming of methanol for high-purity hydrogen production over Cu-MgO/Al2O3 bifunctional catalysts

Sorption enhanced steam reforming of methanol (SESRM) can significantly promote the hydrogen production process with simultaneous CO2 sorption. The mechanical mixture of catalysts and sorbents as a conventional approach is complex and requires high temperatures for regeneration, which results in serious sintering of Cu-based catalysts. This paper describes a novel Cu-MgO/Al2O3 bifunctional catalysts (xCMA, x is denoted as the mass fraction of Cu, 0%–10%) via a sol–gel method for the SESRM process. We find that Cu species, including metallic Cu and Cu ions, co-exist on the catalyst. The metallic Cu on the catalyst surface is an active site for methanol steam reforming while the Cu ion in MgO lattice promotes the CO2 sorption capacity. Moreover, the incorporation of Cu ion into MgO also facilitates CO2 desorption by forming more bidentate carbonates. Due to the strong interaction between Cu and MgO, the Cu sintering is inhabited in comparison with the mechanical mixture of catalysts and sorbents. Meanwhile, MgO is found to induce more formate species to inhibit the generation of carbon monoxide. As a result, the optimal bifunctional catalyst, 8 wt% Cu-MgO/Al2O3 (8CMA) shows a superior performance in both catalytic reforming and CO2 sorption with a highest H2 selectivity of 99.3% and lowest CO selectivity (<0.15%) over 10 repeated cycles. This study suggests that the appropriate control of bifunctional catalysts can lead to powerful potential for high H2 production performance in SESRM.

Chemical and Thermal Sintering of Supported Metals with Emphasis on Cobalt Catalysts During Fischer-Tropsch Synthesis.

This comprehensive critical review combines, for the first time, recent advances in nanoscale surface chemistry, surface science, DFT, adsorption calorimetry, and in situ XRD and TEM to provide new insights into catalyst sintering. This work provides qualitative and quantitative estimates of the extent and rate of sintering as functions of nanocrystal (NC) size, temperature, and atmosphere. This review is unique in that besides summarizing important, useful data from previous studies, it also advances the field through addition of (i) improved or new models, (ii) new data summarized in original tables and figures, and (iii) new fundamental perspectives into sintering of supported metals and particularly of chemical sintering of supported Co during Fischer-Tropsch synthesis. We demonstrate how the two widely accepted sintering mechanisms are largely sequential with some overlap and highly NC-size dependent, i.e., generally, small NCs sinter rapidly by Ostwald ripening, while larger NCs sinter slowly by crystallite migration and coalescence. In addition, we demonstrate how accumulated knowledge, principles, and recent advances, discussed in this review, can be utilized in the design of supported metal NCs highly resistant to sintering. Recommendations for improving the design of sintering experiments and for new research are addressed.

Tailor-Made Zeolitic Water Nanochannels for Liquid Fuel Production

Conversion of CO2 into valuable liquid fuels or other chemicals has been one of the attractive ways for effective utilization of CO2 produced by burning fossil fuels. However, this task is challenging due to the difficulties associated with the chemical inertness of CO2. In addition to research efforts devoted to the development of more active and selective catalysts for CO2 hydrogenation reaction, removing the by-product water from the system is proven beneficial for improving the reaction thermodynamics and kinetics toward desirable products. Therefore, highly water-selective membranes able to operate under reaction conditions like high temperature and pressure have long been pursued. In a recent study, Yu et al. reported a zeolite membrane with gas-impeding water-conduction nanochannels that selectively remove by-product water from CO2 dehydrogenation process, greatly enhancing CO2 conversion and methanol yield.

Efficient and stable supercritical-water-synthesized Ni-based catalysts for supercritical water gasification

Catalyst sintering problem hinders the development of effective supercritical water gasification (SCWG) at milder supercritical water (SCW) temperature for gas fuel production from wet biomass resources. Herein, we prepared a series of supported Ni catalysts by hydrothermal synthesis method particularly operated at the SCW region, and studied the activity and property stability of these newly developed catalysts for SCWG. Supporting materials studied for Ni include ZrO2, Ce-promoted ZrO2, Al2O3, Mg-promoted Al2O3, active carbon and carbon nanotube, and the supercritical water synthesis (SCWS) was conducted at 500 °C, 23 MPa in batch reactor using metallic nitrates as starting feed. SCWG results and catalyst characterization (XRD, SEM-EDS, N2 adsorption/desorption and TGA) confirmed the high activity, superiorly stable crystalline structure and pore structure, and excellent regeneration ability of the SCWS-prepared catalysts (especially Ni/MgO-Al2O3) for SCWG reactions, showing that SCWS is a promising method to develop active and stable catalyst for SCWG process.

Catalyst-Free Partially Bio-Based Polyester Vitrimers

Most of the vitrimers based on ester linkages reported so far contain a Lewis acid or a strong organic base as the transesterification catalyst. The recyclability and reusability of these vitrimers are dependent on the catalyst retention, stability, and sintering issues. Herewith, a set of β-activated ester-based vitrimers are reported that can be thermally reprocessed at ∼150 °C under catalyst-free conditions. The relaxation temperature decreases to 110 °C in the presence of Sn(Oct)2. Importantly, the precursor of these vitrimers, malonic ester, is a cost-effective naturally occurring ester and can be extracted from various fruit juices. As a proof of concept, poly(hydroxyethyl methacrylate) is used as the hydroxyl precursor for the synthesis of vitrimers. These vitrimers display an adequate tensile strength (11.3–33.0 MPa), elongation (80–290%), and resilience. The materials can be effectively self-healed and reprocessed in the presence of heat without sacrificing the tensile properties. The vitrimers b...

Real-time atomistic simulation of the Ostwald ripening of TiO2 supported Au nanoparticles.

Ostwald ripening (OR), one of the major processes of nanoparticle sintering, is critical for the rational design of functional nanomaterials. However, the atomistic mechanism of OR has not been fully understood, because the characterization of interparticle transport of atoms in real-time is challenging by either experiments or theoretical simulations. Thus, current understandings are based on ad hoc assumptions about the OR mechanism, which have never been confirmed yet at the atomic scale. Herein, we realized all-atom kinetic Monte Carlo simulation of sintering of TiO2 supported Au nanoparticles (NPs) through the OR mechanism at millisecond timescales. We demonstrated that the "semi-spherical" assumption should be removed. The OR process was a stagewise process determined by different rate-determining steps, which is in contrast to the single-stage presumption. Au dimers, rather than monomers as generally assumed, were exchanged among different NPs. Besides, we proposed a new kinetic model for describing the determining rate of OR without presumptions. This work brings deeper insights into the atomistic OR mechanism and also paves the way for real-time monitoring of catalyst sintering at the atomic scale.

Enhancing Au/TiO2 Catalyst Thermostability and Coking Resistance with Alkyl Phosphonic-Acid Self-Assembled Monolayers.

Metal oxide-supported Au catalysts, particularly those with small Au nanoparticles, catalyze a variety of reactions including low-temperature CO oxidation and selective hydrogenation of alkynes. However, the facile nature of Au particle growth at even moderate temperatures poses significant challenges to maintaining catalyst activity under reaction conditions. Here, we present a method to reduce the rate of sintering and coke formation in TiO2-supported Au catalysts via the deposition of alkyl-phosphonic acid (PA) self-assembled monolayers. After surface modification with PAs, the resultant catalysts exhibited significantly improved resistance to Au sintering. PA deposition strongly suppressed CO oxidation rates, consistent with poisoning of active sites. In contrast, modification with PAs significantly improved the rate of C2H2 hydrogenation on Au/TiO2. The enhanced activity was accompanied by a dramatically improved resistance to accumulation of surface carbonaceous species.

Parametric Study of CO2 Methanation for Synthetic Natural Gas Production

The production of methane by carbon dioxide hydrogenation through optimization of the operating parameters to enhance methane yield and carbon dioxide conversion in a two‐stage fixed bed reactor is investigated. The influence of temperature, gas hourly space velocity (GHSV), and H2:CO2 ratio on the production of methane is studied. In addition, different methanation catalysts in terms of metal promoters and support materials are investigated to maximize methane production. The results show that the maximum methane yield and maximum carbon dioxide conversion are obtained at a catalyst temperature of 360 °C with a H2:CO2 ratio of 4:1 and total GHSV of 6000 mL h−1 g−1catalyst and reactant GHSV of 3000 mL h−1 g−1catalyst. The optimum metal‐alumina catalyst investigated for CO2 conversion and methane yield is the 10 wt%‐Ni‐Al2O3 catalyst. However, reduction in the methane yield is observed with the addition of Fe and Co promoters because of catalyst sintering and nonuniform dispersion of metals on the support. Among the different catalyst support materials studied, i.e., Al2O3, SiO2 and MCM‐41, the highest catalytic activity is shown by the Al2O3 catalyst with 83 mol% CO2 conversion, producing 81 mol% CH4 with 98% CH4 selectivity.

Enhancing catalytic CH4 oxidation over Co3O4/SiO2 core–shell catalyst by substituting Co2+ with Mn2+

Co3O4, a transition metal oxide with spinel structure, has attracted wide attention due to its high catalytic activity in the field of catalytic oxidation of low concentration methane. However, due to the harsh conditions of methane catalytic reaction on catalysts, of which the high reaction temperature and complex reaction environment often lead to the deactivation and sintering of Co3O4 catalyst, improving the comprehensive performance of Co3O4 catalyst has become the current research hotspot and urgent demand. Core-shell flower-spheroidal cobalt-manganese composite catalyst was prepared in this paper by hydrothermal method, which gave full play to the advantages of carrier, special morphology and doping modification, reduced the risk of sintering and deactivation of Co3O4, and showed higher catalytic activity. Through SEM, EDS, and BET test and analysis, Mn1/Co/SiO2 has better microstructure and structure than Co3O4/SiO2. For example, the dispersion of Mn1/Co/SiO2 and the uniform distribution of elements are higher, and the values of surface area and pore volume are larger (129.956 m2/g → 180.639 m2/g, 0.333363 cm3/g → 0.398030 cm3/g). Combined with XRD and XPS analysis, it is concluded that Mn2+ manganese ion replaces Co2+ and causes lattice distortion of Co3O4, which promotes the production and mobility of reactive oxygen species, further increasing catalytic activity. Compared with Co3O4/SiO2, methane conversion at 350 °C and 450 °C increased by 10% and 6%, respectively.

Cu-K/Al2O3 based catalysts for conversion of carbon dioxide to methane and carbon monoxide

A series of Cu-K/Al2O3 catalysts were synthesized by wet impregnation technique. The reduced catalysts were further used for conversion of carbon dioxide to methane and carbon monoxide. Moreover, the fresh and used catalysts were characterized to investigate the changes in the surface morphology, metal dispersion, surface area, crystalline phases, and functional groups of studied catalysts. The SEM analysis of fresh and spent catalysts showed no remarkable difference in surface morphology with irregular shaped agglomerated particles. Furthermore, TEM micrographs presented the well distribution of metal catalyst over alumina support. The decrease in surface area from 115 to 77 m2/g for Cu1.62-K0.5/Al2O3 after reaction was related to sintering and oxidation of catalyst during reaction. XRD revealed the disappearance of some minor peaks which can be associated with the sintering of spent catalyst. FTIR also presented some new peak for spent catalyst which can be linked with metal oxides. Moreover, various reaction conditions of temperature (230, 400, and 600 °C), pressure (1 and 7 bar), and feed molar ratio of H2/CO2 (2:1 and 4:1) were investigated using different Cu loading (0, 1, 1.25, 1.62, and 4 weight percent). A maximum CO2 conversion of 63% with 39% CH4 selectivity was achieved by using Cu1.62-K0.5/Al2O3 at 600 °C, molar ratio of H2/CO2 4 under 7 bar. The presence of K on the surface of synthesized catalyst increased the CO2 conversion from 48% (Cu1/Al2O3) to 55% (Cu1-K0.5/Al2O3) at above mentioned reaction conditions which suggested the promoter effect of K during conversion of carbon dioxide.

The Role of Nitrogen and Boron Dopants Incorporated in Carbon Nano Onions Toward Electrocatalytic Oxygen Reduction Reaction

Oxygen reduction reaction (ORR) is an essential reaction in fuel cells and metal-air batteries. One main challenge in these energy conversion and storage devices is the sluggish kinetics of ORR at the cathode. It is required that ORR electrocatalysts should operate under low overpotential giving high current density for an extended running time. To date, platinum (Pt)-based catalysts are the most efficient electrocatalyst for ORR with high current density. However, Pt catalysts still suffer from high over-potential, instability and surface poisoning during their electrochemical operations. Furthermore, Pt is expensive and has a limited abundance on earth. Thus, the development of an alternative catalyst is imperative. A novel material should be metal-free, cheap, efficient and stable over a long period of time. Now, intensive endeavors have been taken to replace Pt with heteroatom co-doped carbon catalysts. For instance, nitrogen (N) and boron (B) heteroatoms are incorporated in carbon-based host materials such as graphene sheets, graphene nanoribbon, and carbon nano-onions (CNOs). However, the fundamental understanding of catalyst active sites associated with doped heteroatoms is limited, and further studies are necessary to develop catalysts to replace Pt-based catalysts. CNOs are an emerging type of carbon allotropes. CNOs are comprised of concentric sp2-carbon bonded, graphitic shells surrounding a hollow core. Especially, nanodiamond-derived CNOs are <10 nm in diameter. These particular CNOs have a high specific surface area (~ 300 m2/g) and a good electrical conductivity. Furthermore, the curved graphitic shells of CNOs elevate the electron density of outer surfaces and generate a strain, promoting electrocatalytic activity. In the present study, CNOs was selected as a substrate for the incorporation of nitrogen (N) and boron (B) atoms. Briefly, N-doped CNOs (N-CNOs) were first prepared at 700 ºC. Then, B was introduced into N-CNOs. The incorporation of B into N-CNOs was done at varied temperature ranging from 600 ºC to 1000 ºC. The effect of temperature on the chemical states of B and N co-dopants was thoroughly studied. Furthermore, the curvature effect of CNOs on the chemical reactivity toward doping and catalytic activity toward ORR was investigated. The morphology, microstructure, and chemical states of undoped and N, B-doped CNOs (NB-CNOs) were probed by high resolution transmission electron microscopy (HR-TEM), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The electrocatalytic performance of NB-CNOs toward ORR were assessed by a series of electrochemical characterizations including cyclic voltammetry, linear sweep voltammetry, rotating disk electrode (RDE), and rotating ring disk electrode (RRDE) measurements. The electrochemical characterizations were performed in aqueous electrolyte, 0.1 M KOH. RDE measurements were performed at 5 mV/s scan rate and with the rotation speeds between 400 and 3600 rpm. The electron transfer number for the ORR pathway was determined from the Koutecky-Levich analyses of RDE results. Overall, the NB-CNOs prepared at 700 ºC showed the best performance among the prepared NB-CNOs such as highest current density (~ 6 mA/cm2), low onset potential ( -0.05 V vs. Ag/Ag Cl), and the dominant 4-electron transfer. The performance of NB-CNOs prepared at 700 ºC was comparable to that of commercial Pt/C catalyst. Furthermore, N, B-CNOs showed a remarkable long-term stability. This performance was related to active sites formed on CNOs associated with N and B dopants. It was noted that the formation of separated N and B atoms is favored at low temperature and constitutes active sites for ORR. However, the number of these active sites was reduced at elevated temperatures due to catalyst sintering and the aggregation of N and B. As a result, the catalyst performance was degraded with the increase of the annealing temperature. This presentation will address unique synthesis, chemical structure, and electrochemical performances of NB-CNOs. Fundamental knowledge gained on the role of curvature in the heteroatom doping and structure-catalytic activity relations will be highlighted. This knowledge will pave the way for efficient and robust electrocatalysts towards ORR.

CO Oxidation over Metal Oxide (La2O3, Fe2O3, PrO2, Sm2O3, and MnO2) Doped CuO-Based Catalysts Supported on Mesoporous Ce0.8Zr0.2O2 with Intensified Low-Temperature Activity

CuO-based catalysts are usually used for CO oxidation owing to their low cost and excellent catalytic activities. In this study, a series of metal oxide (La2O3, Fe2O3, PrO2, Sm2O3, and MnO2)-doped CuO-based catalysts with mesoporous Ce0.8Zr0.2O2 support were simply prepared by the incipient impregnation method and used directly as catalysts for CO catalytic oxidation. These mesoporous catalysts were systematically characterized by X-ray powder diffraction (XRD), N2 physisorption, transmission electron microscopy (TEM), energy-dispersed spectroscopy (EDS) mapping, X-ray photoelectron spectroscopy (XPS), and H2 temperature programmed reduction (H2-TPR). It was found that the CuO and the dopants were highly dispersed among the mesoporous framework via the incipient impregnation method, and the strong metal framework interaction had been formed. The effects of the types of the dopants and the loading amounts of the dopants on the low-temperature catalytic performances were carefully studied. It was concluded that doped transition metal oxides could regulate the oxygen mobility and reduction ability of catalysts, further improving the catalytic activity. It was also found that the high dispersion of rare earth metal oxides (PrO2, Sm2O3) was able to prevent the thermal sintering and aggregation of CuO-based catalysts during the process of calcination. In addition, their presence also evidently improved the reducibility and significantly reduced the particle size of the CuO active sites for CO oxidation. The results demonstrated that the 15CuO-3Fe2O3/M-Ce80Zr20 catalyst with 3 wt. % of Fe2O3 showed the best low-temperature catalytic activity toward CO oxidation. Overall, the present Fe2O3-doped CuO-based catalysts with mesoporous nanocrystalline Ce0.8Zr0.2O2 solid solution as support were considered a promising series of catalysts for low-temperature CO oxidation.

CO2 reforming with methane reaction over Ni@SiO2 catalysts coupled by size effect and metal-support interaction

CO2 reforming with methane is an attractive reaction to produce syngas and reduce greenhouse gases. The main problems for the reaction are catalyst sintering and carbon deposition at high temperatures. In this study, we fabricated core-shell structured Ni@SiO2 catalysts with ultrafine nickel nanoparticles by microemulsion method. The catalysts were calcined at different temperatures to obtain different sizes of Ni nanoparticles and achieve different strengths of metal-support interaction. CO2 reforming with methane reaction over the Ni@SiO2 catalysts revealed that catalytic performance was dependent on both size of Ni nanoparticles and strength of metal-support interaction. The best coupling of size effect and metal-support interaction in the Ni@SiO2-600 exhibited the highest performance and stability, which was assigned to the maintained smallest size of Ni nanoparticles and the lowest carbon deposition when compared with Ni@SiO2-500 and Ni@SiO2-700 catalysts.

Deactivation by sintering of the cobalt catalyst during the Fischer-Tropsch reaction

In the present work, the deactivation by sintering of cobalt-based catalyst during Fischer-Tropsch synthesis at low temperature was studied by numerical simulation. For this purpose, a mathematical model was developed. The obtained simulation results allowed us to highlight and improve the understanding of the deactivation phenomena of cobalt-based Fischer-Tropsch catalysts by sintering. The main results also show that the sintering phenomenon is strongly dependent on the operating conditions, in particular, the temperature, the pressure, and the H2/CO molar ratio, as well as the reaction by-products such as water. The results obtained can, therefore, be used to understand more the sintering mechanism which may be linked to the change in the concentration of the active sites and the reaction rates.

Nickel-based catalysts for steam reforming of naphthalene utilizing gasification slag from municipal solid waste as a support

Nickel-based catalysts were synthesized using gasification slag as an abundant and inexpensive material with high mechanical strength. The synthesis procedure comprised of etching of gasification slag with hydrofluoric acid, aluminum hydroxide addition, impregnation with Ni and calcination. The naphthalene reforming activity was tested at 850 °C and 24,000 h−1 gas hourly space velocity in the presence of 50 ppmv H2S and 300 ppmv HCl in gas. The presence of aluminum hydroxide and an oxidizing environment during the calcination process were essential for preparation of active catalysts. The addition of 30% of aluminum hydroxide to gasification slag improved the dispersion of Ni oxide and increased the Brunauer–Emmett–Teller (BET) specific surface area determined by N2 adsorption at −196 °C from 4.5 to 15.0 m2 g−1 as compared to the catalyst without aluminum hydroxide. This resulted in the increased naphthalene conversion from 35 to 86%. The activity of Ni in synthesized slag catalyst was approximately 3.2 times higher than in commercial catalyst due to the deposition of Ni on the outer surface of catalyst particles. The deposited Al and Ni species were firmly attached to the slag particles during calcination at 500–1000 °C. While high calcination temperature was beneficial for high mechanical strength of catalyst, the procedure should be conducted under oxidizing environment. When calcination was carried out in N2 environment at 1000 °C, the sintering of catalyst particles and encapsulation of Ni occurred, which drastically decreased the BET specific surface area to 0.4 m2 g−1 and naphthalene conversion to 30%. These negative effects could be prevented when air was used during calcination, which facilitated earlier crystallization and inhibited excessive sintering of catalyst, thus, maintaining the high catalytic activity.