Study on solid waste pyrolysis coke catalyst for catalytic cracking of coal tar

Low value solid waste pyrolysis coke was used as a catalyst to catalytically crack gas-phase tar to improve tar yield and gas production. Pyrolysis coke with different pyrolysis final temperature and pyrolysis time were prepared, the effect of tar cracking products was studied, and the optimal pyrolysis coke were screened. The pyrolysis coke catalyst was characterized by BET, FTIR, SEM. The results show that the optimal preparation final temperature of pyrolysis coke is 750 °C, and the optimal preparation pyrolysis time is 2 h. Compared with the pyrolysis of raw coal, the tar cracking rate increased by 9.3%, after added the pyrolysis coke catalyst, the gas increased by 23.2%, and the light component increased to 36.6%. And the OH, C–N and C–O–C functional groups present on coke are the factors that affect the catalytic cracking.     

Effect of synthesis temperature on catalytic activity and coke resistance of Ni/bio-char during CO2 reforming of tar

Understanding how the synthesis parameters affect nickel particle distribution is critical to the synthesis of Ni/bio-char with excellent catalytic performance. In this work, the influence of synthesis temperature on catalytic activity and coke resistance of Ni/bio-char during CO₂ reforming of tar was explored. With the increase of synthesis temperature from 200 °C to 250 °C, the dispersion of nickel precursor into bio-char was promoted, resulting in an increase in crystallite size of metallic nickel particle from 51.98 nm to 62.45 nm. Besides, parts of the metallic nickel particles were oxidized to nickel oxides, providing more lattice oxygen to oxidize the coke deposited on the catalyst. However, further increasing the synthesis temperature to 300 °C would aggravate the oxidation of active nickel particles. The increase in crystallite size of nickel oxide particle from 23.25 nm to 43.38 nm could block the pore structure and hinder the access of reactants, resulting in a drop in the tar conversion rate from 40-51% to 13–27%.     

Cu2-xSe@CuO core-shell assembly grew on copper foam for efficient oxygen evolution

Hydrogen production from electrolyzed water is a mature technology and has great development prospects in terms of energy conversion and utilization. However, the kinetically sluggish oxygen-evolution reaction becomes the limiting step in the electrolysis of water. Copper-based materials have been reported as a good choice to catalyze the oxygen evolution reaction, but their performance is poor. We describe a Cu_2-xSe@CuO/copper foam core–shell structure from the in situ electrochemical oxidation of Cu₂Se/copper foam to promote the oxygen-evolution reaction performance. The presence of a semi-metallic Cu_2-xSe core and nanostructured CuO shell at a current density of 10 mA cm⁻² requires a low overpotential of 253 mV. The Tafel slope was only 73 mV dec⁻¹. The preparation of Cu_2-xSe@CuO on three-dimensional copper foam facilitates the reaction.     

One-step synthesis of biochar-supported potassium-iron catalyst for catalytic cracking of biomass pyrolysis tar

In this work, K–Fe bimetallic catalyst supported on porous biomass char was synthesized via a one-step synthesis method by pyrolysis of biomass (peanut shells) after impregnation of a small amount of potassium ferrate (PSC–K₂FeO₄), and was evaluated for the cracking of biomass pyrolysis tar. Control experiments using the pure char (PSC) and char-supported catalysts after impregnation of KOH (PSC–KOH) and FeCl₃ (PSC–FeCl₃) were also performed for comparison. The as-prepared PSC-K₂FeO₄ possessed a porous structure with the dispersion of particles/clusters of Fe metal, K₂CO₃ and KFeO₂ on the char support. Tar cracking experiments showed that the PSC-K₂FeO₄ exhibited excellent catalytic activity on the cracking of biomass pyrolysis tar in the temperature range of 600–800 °C, and the obtained tar conversion efficiencies were obviously higher than that in the control experiments, particularly at relatively lower temperatures (600 and 700 °C). The yields of combustible gas compounds including CO, H₂ and CH₄ increased significantly using PSC-K₂FeO₄ as the catalyst due to the enhanced tar cracking and reforming reactions. The porous structure and the active crystal structures of the spent catalyst were well retained, indicating the potential for efficient and long-term utilization of the catalyst in tar cracking. PSC-K₂FeO₄ exhibited excellent reusability during the five times reuse under the same conditions without regeneration, which showed almost no obvious decrease in the tar conversion efficiency and gas yields.     

Ni/SiO2 core–shell catalysts for catalytic hydrogen production from waste plastics-derived syngas

Ni/SiO₂ core–shell catalysts were prepared by deposition–precipitation method and used to produce hydrogen from waste plastics-derived syngas. The SiO₂ core synthesized by the Stöber process was used as the support. This core was synthesized using various solvents, and the effect of these solvents on the morphologies and catalytic performance of the Ni/SiO₂ core–shell catalysts was investigated. The synthesis parameters of the Ni/SiO₂ catalysts were further investigated to enhance the metal–support interaction and dispersion of Ni on the SiO₂ support. The highest catalytic activity of 181 mmol/g-h was achieved when the Ni/SiO₂ core–shell catalyst was synthesized in methanol (Ni/SiO₂–M) and reacted at 800 °C at a water-addition rate of 0.75 g-H₂O/h. The Ni/SiO₂–M catalyst, which possessed strong metal–support interaction nickel phyllosilicates, high specific area, small particle size, and homogeneous metal dispersion, exhibited the best long-term stability.     

镍基镁渣催化剂对生物质焦油模化物催化重整特性实验研究

采用湿浸渍法制备Ni/γ-Al₂O₃和Ni/MS(magnesium slag)催化剂,选择糠醛、甲苯、萘、芘作为生物质焦油的模化物,研究不同镍基催化剂对四类焦油模化物在固定床反应器内进行催化重整的重整特性。结果表明,Ni/MS催化剂在催化所有模化物的重整反应时,气相碳转化率和气体产率均明显高于Ni/γ-Al₂O₃催化剂。当水分子物质的量与碳原子物质的量之比为1.5时,糠醛的气相碳转化率达到最高值86.54%。X 射线衍射 (XRD)结果表明,Ni/MS催化剂上存在的多种固溶体（NiO-Fe₂O₃、NiO-MgO）形成了多种活性位点。     

Roles of AAEMs in catalytic reforming of biomass pyrolysis tar and coke accumulation characteristics over biochar surface for H2 production

Coke formation is a significant challenge in catalytic tar reforming. AAEMs are essential in the conversion and decomposition of tar catalyzed by biochar. In this paper, four biochar catalysts with different K and Ca contents were prepared by acid washing and loading, and the coke accumulation characteristics in catalytic tar reforming at 650 °C were investigated using a single-stage reaction system. The gas-liquid-solid products were characterized by GC-MS, Raman, N₂ adsorption, FTIR and TG. The results suggest that K-loaded biochar has a maximum tar reforming capacity of 94.9%, while H-form biochar has a tar removal efficiency of only 27.8%. The micropore area in biochar is considerably reduced and the average pore size is increased after coke deposition. While K-loaded biochar retains the highest micropore area, it also exhibits a smaller increase in average pore size. The loading of K/Ca affects the growth structure of the coke, resulting in an increased number of O-containing structures in it. The coke on the Raw biochar surface is mainly small aromatic ring structures and aliphatic structures, thus increasing the intensity of the vibrational peaks corresponding to aromatic = C–H and aliphatic C–H on it. The coke on K-loaded biochar has a large proportion of aliphatic structures, which also contributes to the reduced graphitization of it after reforming. The AAEMs-free biochar surface preferentially removes tar components carrying O-containing groups. K-loaded biochar preferentially catalyzes the reforming of mono-aromatic ring components in tar. Ca-loaded biochar preferentially removes the mono-aromatic ring components, while being less selective for the removal of tar components containing hydroxyl groups and polyaromatic ring components. The loading of K/Ca promotes the dehydrogenation of the tar fraction during reforming, while only K catalyzes the deoxygenation of tar components. H-form biochar has no appreciable catalytic activity on CH₄ cracking. AAEMs have a catalytic activity on CH₄ cracking. K is particularly effective in improving tar conversion and hydrogen production of biochar.     

Enhancement of the catalytic performance and coke resistance of alcohol-promoted Ni/MCM-41 catalysts for CH4/CO2 reforming

A series of Ni-based catalysts were prepared by the alcohol-promoted impregnation for CO₂ reforming of methane. In order to illuminate the effects of carbon chain numbers and hydroxyl group numbers on the catalytic performance and coke resistance of Ni-based catalysts, the samples were characterized by XRD, SEM, BET, H₂-TPR, FT-IR, XPS, TG, and TEM. The results show that the introduction of alcohol during impregnation promotes Ni²⁺ species into the channels of MCM-41, thereby strengthening the meatal-support interaction. Besides, the presence of alcohol decreases the particle size of Nickel and increases the surface adsorbed oxygen species over the surface of the support, thus promoting the coke resistance of the catalysts. As a consequence, NM-EG shows the highest catalytic performance, the highest stability, and the best coke resistance in all of the catalysts. This indicates that the main factor influencing the catalytic performance and coke resistance of the catalysts is the number of hydroxyl groups rather than the chain length of the introduced alcohol in the alcohol-promoted impregnation.     

Construction of high-performance NiCe-MOF derived structured catalyst for steam reforming of biomass tar model compound

High-performance and inexpensive catalysts play a large role in effective removal of biomass tar produced during biomass gasification. In this study, raw wood, with long, through, but distorted channels and a low tortuosity, was selected as a support. A layered NiCe-metal organic framework (NiCe-MOF) was grown in-situ on the surface of raw wood microchannels by using abundant surface hydroxide groups. Then, this catalyst was carbonized at 600 °C in a N₂ atmosphere to obtain NiCe-MOF derived catalyst/wood carbon (NiCe-MDC/WC), which was selected as a structured reactor for the steam reforming of biomass tar. NiCe-MDC/WC achieved an excellent conversion rate of approximately 99% for toluene and a high catalytic stability of 48 h at low temperature of 550 °C. Moreover, NiCe-MDC/WC showed higher catalytic performance than Ni-MDC/WC (～79%), crushed-NiCe-MDC/WC (～94%), and Ni/WC (～75%) in stability tests. These excellent results were assumed to be derived from the multilevel structure obtained from wood carbon microchannels and secondary layered MOF channels, appropriate metal-support interactions, and the presence of Ce, which could improve the dispersion of active sites and mass transfer efficiency and inhibit coke formation. Thus, such Ni-based MOF-derived structured reactors are promising for tar conversion and useful syngas production.     

Effect of CO2 atmosphere on biomass pyrolysis and in-line catalytic reforming

To enhance the conversion efficiency of biomass CO₂ gasification and decrease tar, the experimental study of biomass pyrolysis and in-line catalytic CO₂ reforming (BPy-ILCCR) were investigated in a two-stage reactor. The prepared K-Ni/Al catalyst exhibits superior catalytic activity for gas products in BPy-ILCCR. Results show that both CO₂ concentration and temperature promote the rise of the gas production, but the increase slows down when CO₂ concentration is more than 40 vol%. At 700°C, the gas yield and X_c can reach 0.83 g/g-bio and 92.4%, respectively (40 vol% CO₂, 3 g catalyst). The comparative study indicates that steam is slightly better for reducing liquid product under the same concentration of CO₂ and H₂O, and the X_c at 80 vol% CO₂ can reach 93.9%, close to the value obtained at 40 vol% H₂O. Moreover, there exist similar quantities of coke deposition on the catalyst under the CO₂ and H₂O atmosphere.     

The influence of preparation method of char supported metallic Ni catalysts on the catalytic performance for reforming of biomass tar

The char‐supported nickel catalysts prepared by wet impregnation and precipitation‐deposition methods under different nickel loadings and catalytic temperatures for catalytic reforming of rice husk tar were investigated. The influences of preparation methods on the physicochemical properties of catalysts and catalytic activity towards tar conversion and gas yield were studied. The results showed that char‐supported metallic Ni catalysts can be directly used without a reduction process because of carbon thermal reaction during calcination. The preparation method had a significant influence on the porosity and Ni dispersion of catalysts. The addition of Ni to char improved the specific surface area from 60 m² g^?1 to 346.8 m² g^?1 because of activation effect of nickel nitrate on char pore structure. The precipitation‐deposition method produced higher surface area, smaller Ni nanoparticulates with more corner and step sites, as well as more concentrated size distribution than those of wet impregnation method, leading to higher catalytic activity, in terms of high tar conversion efficiency (83%) and increasing syngas yield. The selectivity to phenols and naphthalene for precipitation‐deposited catalysts was strengthened, and the relative content of heavy tars was decreased remarkably. The increasing H₂ yield and concentration were indicative of efficient conversion of macromolecular organic matters into small molecules gases. In addition, the precipitation‐deposited catalyst exhibited weaker Ni sintering after reaction. The catalytic cracking temperature of 800° C and Ni loading of 10 wt% exhibited the best catalytic effects on gas distribution and tar conversion.     

A novel hybrid iron-calcium catalyst/absorbent for enhanced hydrogen production via catalytic tar reforming with in-situ CO2 capture

An iron-calcium hybrid catalyst/absorbent (Ca–Al–Fe) is developed by a two-step sol-gel method to enhance tar conversion, cyclic CO₂ capture and mechanical strength of absorbent for hydrogen production in calcium looping gasification. The developed catalyst/absorbent consists of CaO and brownmillerite (Ca₂Fe₂O₅) with mayenite (Ca₁₂Al₁₄O₃₃) as inert support. Comparing with three candidate absorbents without Ca₂Fe₂O₅ or Ca₁₂Al₁₄O₃₃, cyclic carbonation reactivity and mechanical strength of Ca–Al–Fe are largely promoted. Meanwhile, Ca–Al–Fe approaches the maximum conversion rate of 1-methyl naphthalene (1-MN) with enhanced hydrogen yield around 0.15 mol/(h·g) under reforming conditions of present study. Ca–Al–Fe also shows the largest CO₂ absorption and lowest coke deposition. Influences of operation variables on 1-MN reforming are evaluated and recommended conditions can be iron to CaO mass ratio of 10%, reaction temperature of 800 °C and steam to carbon in 1-MN mole ratio of 2.0. Ca–Al–Fe hybrid catalyst/absorbent presents good potential to be applied in future.     

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.     

Experimental comparison of biochar species on in-situ biomass tar H2O reforming over biochar

Experimental investigations of in-situ tar H₂O reforming over various biochar species were carried out in the two-stage fluidized bed/fixed bed reactor. The physicochemical structures of biochar were studied by SEM, mercury intrusion porosimetry and FTIR methods. The mechanism of tar H₂O reforming over biochar was studied through the results of tar yields and quantitative analysis of typical tars by GC/MS. According to the theory of organic mass spectrometry and current mechanisms of tar transformation, the reaction path of typical tar H₂O reforming over biochar was constructed. The results show that the tar reforming rate over sawdust biochar is the most significant among the three kinds of biochar samples (i.e., rice husk, sawdust and cornstalk). The metallic species contribute greatly to the weight loss of biochar in 15 vol% H₂O atmosphere at 800 °C, while they are not the only determinants of tar H₂O reforming. The selectivity of biochar on the in-situ tar H₂O reforming is determined by the coupling effects of its physical and chemical characteristics. The biochar, with the porous surface structures, a certain amount of metallic species and the carbon structure with low polymerization, would be effective on in-situ tar H₂O reforming.     

Hydroxyl-promoter on hydrated Ni-(Mg,Si) attapulgite with high metal sintering resistance for biomass derived gas reforming

As hydrated magnesium-aluminum-silicate crystals, attapulgite and HNO₃/NaOH pretreated attapulgite were used as support to prepare nickel-based catalysts via ultrasonic-assisted impregnation method. The as-prepared catalysts were employed in the biomass derived gas (especially CO₂ and CH₄) reforming with a considerable catalytic performance achieved (CH₄ conversion: 75.26%, CO₂ conversion: 85.75%) over HNO₃-attapulgite (10% Ni) at 700 °C and GHSV of 36000 mL/g.h during 600 min, demonstrating the potential of modified attapulgite as support applied in catalytic reforming. According to the characterization results obtained from BET/FT-IR/H₂-TPR/XRD/SEM/TPO, it was found that the formation of (Ni, Mg) containing phyllosilicate improved metal sintering resistance by the confinement effect. Besides, FT-IR results illustrated the existence of hydroxyl in the catalyst structure, which was beneficial for inhibiting the Boudouard side reaction, further enhancing the carbon resistance of catalysts. Moreover, TPO results showed that the deposited carbon on modified attapulgite was mainly fibrous carbon which can be removed easily, thus maintaining the catalytic performance. Due to its unique structure and high metal sintering resistance, it is believed that the attapulgite supported catalyst can be used in any other catalytic reforming process such as steam reforming of methane.     

Ni-based catalysts with coke resistance enhance by radio frequency discharge plasma for CH4/CO2 reforming

Coke deposition has been considered to be one of the most important reasons hindering the stability of the catalyst during CH₄/CO₂ reforming. In this study, after the addition of P123 (PEG-PPG-PEG triblock copolymer), Ni²⁺ can be well-dispersed on the mesoporous molecular sieve MCM-41. And then, the catalysts were prepared by using N₂ radio frequency (RF) discharge plasma for different treatment times to reduce the size of Ni particles, improve the anti-coking performance, and thereby improve the stability of the catalyst. The results showed that the catalyst NM-P123-PN2h exhibits superior catalytic properties in the CH₄/CO₂ reforming. The initial conversions of CH₄ and CO₂ were 90.80% and 89.60% at 750 °C, respectively. The catalyst NM-P123-PN2h showed highly coke resistance with less carbon deposition (1.12%) at 750 °C after 10 h of continuous reaction, while the carbon deposition of the catalyst NM-C was 37.32%. Compared with the traditional calcination method, the catalyst prepared by plasma treatment has a smaller particle size and better dispersibility of nickel. In particular, the nickel particle size of the catalyst NM-C was 8.37 nm, however, that of the catalyst NM-P123-PN2h was only 1.70 nm, and the nickel particle size was reduced by 5 times. Therefore, it can be concluded that the catalyst prepared under the combined action of P123 and RF plasma-treated can effectively improve the coke resistance of the catalyst and the stability of the CH₄/CO₂ reforming.     

Development of nanosilica-based catalyst for syngas production via CO2 reforming of CH4: A review

The alarming global warming issue has sparked interest in researchers to mitigate greenhouse gas emissions via CO₂ reforming of CH₄ (CRM). Regrettably, the main drawback of CRM is catalyst deactivation because of coking and metal sintering. Therefore, exceptional resistance towards coking and sintering is crucial to formulate viable CRM catalysts. This article reviewed the latest development of nanosilica-based catalysts (mesoporous nanosilica, dendritic fibrous nanosilica, green nanosilica, and core@shell nanosilica) for CRM application. The physicochemical properties of nanosilica supports could be modulated by synthesis methods to improve their resistance towards coking and sintering. Furthermore, this review compiled the influence of catalytic properties of nanosilica supported catalysts, such as active metal dispersion, crystallite size, acid-basic properties, oxygen mobility, reducibility, porosity, and morphology on CRM. To conclude, nanosilica supports with strong metal-support interaction, homogeneous metal dispersion, appropriate crystallite size, and moderate acidity/basicity, exhibited satisfactory catalytic activity, thermal stability, and resistance towards coking and sintering. The fundamental study and depth understanding on this catalysis field is of worth in configuring robust catalysts for future industrial applications success of CRM reaction with superb activity and carbon resistance for CRM.     

Sequence of Ni/SiO2 and Cu/SiO2 in dual catalyst bed significantly impacts coke properties in glycerol steam reforming

Coke formation is a major challenge in steam reforming reactions. In addition to development of robust catalyst for tackling coking, in this study we explored the approach of using dual catalyst bed with the catalyst on top as the guard or sacrifice catalyst while with the bottom catalyst to catalyze the steam reforming. The rationale is that some oxygen-containing reactants are prone to polymerize on heating, and the polymeric coke could directly fall on surface of catalyst and leads to the rapid deactivation. Hence, glycerol was selected as the reactant for steam reforming in the catalyst bed with the Cu/SiO₂ placed on the top of Ni/SiO₂ catalyst. Our results demonstrate that first contact of glycerol to Cu/SiO₂ on top changed abundance/type of small intermediates and the π-conjugated oligomers reached the Ni/SiO₂ catalyst, rendering the Ni catalyst with a higher resistivity towards coking and deactivation. In addition, the carbon nanotube form of coke over Ni/SiO₂ was thinner in wall thickness and larger in inner diameter of the cavity due to the impact of D-Cu/SiO₂. Substantial polymeric coke with amorphous structure and low thermal stability formed over Cu/SiO₂ via polymerisation of reaction intermediates. The characterization (in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS)) for the glycerol steam reforming indicated that the Cu/SiO₂ and Ni/SiO₂ catalyst induced the formation of the very different functionalities of the reaction intermediates.     

Ceria-promoted Ni@Al2O3 core-shell catalyst for steam reforming of acetic acid with enhanced activity and coke resistance

A series of Ni@Al₂O₃ core-shell catalysts with ceria added to the surface of Ni nanoparticles or inside the alumina shell were prepared, and the effect of ceria addition on the performance of the catalyst in the steam reforming of acetic acid was investigated. The prepared catalysts were characterized by BET, XRD, HRTEM, H₂-TPR and DTG. The addition of ceria to the surface of nickel nanoparticles greatly enhanced the activity of catalyst owing to the presence of the mobile oxygen, which migrated from the ceria lattice. Among the prepared catalysts, the Ni@Al10Ce catalyst showed the highest activity with a conversion of acetic acid up to 97.0% even at a low temperature (650 °C). The molar ratio of CO₂/CO was also improved due to the oxidation of CO by the mobile oxygen into CO₂. The coke formation on the core-shell catalysts was significantly inhibited by the addition of ceria to the surface of nickel nanoparticles due to the oxidation of carbon species by the mobile oxygen in the ceria lattice. However, the Ni@Al10Ce-a catalyst with ceria added to the alumina shell showed a low activity and the formation of a large amount of coke. It is suggested that only the ceria in close to the Ni surface has the promoting effect on the catalytic performance of the Ni@Al₂O₃ catalyst in the steam reforming of acetic acid.