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。     

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.     

The performance of nickel-loaded lignite residue for steam reforming of toluene as the model compound of biomass gasification tar

Tars should be removed from biomass gasification systems so as not to damage or clog downstream pipes or equipment. In this paper, lignite insoluble residue (LIR) after extraction of humic acids was used as the support to prepare a nickel-loaded LIR (Ni/LIR) catalyst. This novel catalyst Ni/LIR was tested in steam reforming of toluene as a model compound of biomass tar conducted in a laboratory-scale fixed bed reactor. When compared to the reactions without catalyst or with Ni/Al₂O_3, Ni/LIR was confirmed as an active catalyst for toluene conversion at a relatively low temperature of 900 K. The investigated reforming parameters during the experiments in this research were selected as reaction temperature at a range of 850–950 K, steam/carbon molar ratio at a range of 2–5 mol/mol, and a space velocity from 1696 to 3387 h^?1. It was concluded that, under optimum conditions, significant amount of syngas yields, acceptable Ni/LIR consumption and more than 95% of toluene conversion can be obtained from the biomass Ni/LIR catalytic gasification system.     

Catalytic steam reforming of tar for enhancing hydrogen production from biomass gasification: a review

Presently, the global search for alternative renewable energy sources is rising due to the depletion of fossil fuel and rising greenhouse gas (GHG) emissions. Among alternatives, hydrogen (H₂) produced from biomass gasification is considered a green energy sector, due to its environmentally friendly, sustainable, and renewable characteristics. However, tar formation along with syngas is a severe impediment to biomass conversion efficiency, which results in process-related problems. Typically, tar consists of various hydrocarbons (HCs), which are also sources for syngas. Hence, catalytic steam reforming is an effective technique to address tar formation and improve H₂ production from biomass gasification. Of the various classes in existence, supported metal catalysts are considered the most promising. This paper focuses on the current researching status, prospects, and challenges of steam reforming of gasified biomass tar. Besides, it includes recent developments in tar compositional analysis, supported metal catalysts, along with the reactions and process conditions for catalytic steam reforming. Moreover, it discusses alternatives such as dry and autothermal reforming of tar.     

Chemical looping dry reforming of benzene as a gasification tar model compound with Ni- and Fe-based oxygen carriers in a fluidized bed reactor

Gasification tar during a fluidized bed operation impedes syngas utilization in downstream applications. Among tar constituents sampled during biomass gasification, benzene was the most abundant species. Thus, benzene was used as a model compound for chemical looping dry reforming (CLDR) over iron (Fe) and nickel (Ni) metals impregnated on silicon carbide (SiC) in a lab-scale fluidized bed reactor to convert it into hydrogen and carbon monoxide (H₂ and CO). A high benzene conversion rate (>90%) was observed at a higher experimental temperature (above 730 °C). Catalytic conversion of benzene using NiFe/SiC catalyst resulted in higher H₂ production whereas higher levels of CO were produced with Fe/SiC catalyst at an elevated temperature. Control experiments using an empty bed and SiC bed showed the formation of both the biphenyls and excessive carbon deposits. Air oxidation was also performed for the regeneration of oxygen carrier during the chemical looping operation.     

Steam reforming of toluene as model biomass tar to H2-rich syngas in a DBD plasma-catalytic system

Biomass tar is one of the most troublesome issues limiting the further development of biomass pyrolysis and gasification. In this study, a plasma enhanced catalytic steam reforming technology was applied for biomass tar removal. Toluene was selected as biomass tar surrogate. The nano-sized alumina-supported nickel and iron catalysts with different molar ratios of M/Al (M: Ni or Fe, 0:1, 1:3, 1:1, 3:1, 1:0) were prepared for catalytic steam reforming of toluene in a non-thermal plasma reactor featuring dielectric barrier discharge (DBD). The results showed that syngas was the dominant gas product of toluene decomposition. The conversion efficiency of toluene and energy efficiency using Ni-Al and Fe-Al catalysts both followed a sequence: M1Al3 > M1Al1 > M3Al1, which is in line with the BET surface area and pore volume. However, the selectivity of H₂ and CO catalysed by Ni-Al and Fe-Al catalysts follows the order of M1Al3 < M1Al1 < M3Al1. Presumably, toluene dissociation is a process composed of adsorption-reaction-desorption. The formation of syngas is supposed to proceed as a series of ionic and free radical reactions occurring preferably in the gas phase. Ni1Al3 catalyst shows the largest potential in converting biomass tar into H₂-rich syngas, with a maximum toluene conversion of 96% and a largest H₂ yield of 2.18 mol/mol-toluene. Besides, the results showed that this hybrid plasma-catalysis system was potential in anti-carbon deposition.     

Steam reforming reactions over a metal-monolithic anodic alumina-supported Ni catalyst with trace amounts of noble metal

A trace amount of noble metal (Ru or Pt <0.1 wt%) was doped onto an anodic alumina-supported Ni catalyst, to investigate its performance in the steam reforming of methane (SRM), especially during DSS (daily startup and shutdown) operation. Although the steam purge treatment at high temperatures seriously deactivated the Ni catalyst because of the oxidation of metallic nickel with steam into Ni²⁺, trace Ru assisted the regeneration of active metallic nickel by hydrogen-spillover. And, the Ni sintering was largely alleviated by the addition of Ru, and it was probably due to the formation of Ru-Ni alloy. In comparison with the Ru-doped Ni catalyst, the Pt-doped Ni catalyst showed a more favorable tolerance to steam oxidation, even at 900 °C. In a stationary SRM test of 3000 h and a DSS SRM test of 500 times where the town gas 13A was used as hydrogen source, no obvious deterioration was detected over the Pt-doped Ni catalyst. Especially, when electrically heating the plate-type Pt-doped Ni catalyst to 700 °C, the SRM reaction system could reach a stable state within ca. 10 min, which offered a strong possibility to shorten the startup time from the 1-2 h of conventional reformer to just few minutes. In addition, the noble metal-doped Ni catalyst also showed favorable activity and durability when being applied to other steam reforming systems, such as kerosene and ethanol.     

Experimental study of Ni/MgO catalyst in carbon dioxide reforming of toluene,a model compound of tar from biomass gasification

An experimental study of Ni/MgO solid solution catalyst in CO₂ reforming of toluene was conducted in this paper. Experimental parameters were reduction temperature, reaction temperature, CO₂/toluene mole ratio, and toluene feed rate.     

Development of activated biochar supported Ni catalyst for enhancing toluene steam reforming

Catalytic steam reforming of tar is considered to be an attractive pathway for tar removal and H₂ production in the modern world. In this study, activation of biochar (B) from pine wood pyrolysis was performed to boost its specific surface area and pore structure. The activated biochar (AB) was used as a catalyst support with the aim to enhance the catalytic activity. The catalytic reforming performance of toluene over Ni/AB catalyst was investigated, and the catalytic behavior of Ni/AB catalysts was compared with Ni/Al₂O₃ and Ni/B. The effect of potassium hydroxide (KOH) to biochar ratio, Ni loading, reforming temperature, weight hourly space velocity and steam to carbon ratio(S/C) on the performance of Ni/AB catalysts were studied. The results showed that Ni/AB catalysts exhibited a superior catalytic activity for carbon conversion and H₂ production to Ni/B and Ni/Al₂O₃ catalysts. In addition, high carbon conversion (86.2%) and H₂ production (64.3%) can be achieved with Ni/AB catalyst under the optimal operating conditions. Furthermore, in order to improve the stability of the Ni/AB catalyst, Ce was introduced to Ni/AB catalyst. According to stability tests, the H₂ concentration of Ni-Ce/AB catalysts was still higher than 2.24 mmol/min even after 20 hours reaction.     

Influence of bed material coatings on the water-gas-shift reaction and steam reforming of toluene as tar model compound of biomass gasification

A promising technology replacing fossil energy carriers for the production of electricity, heat, fuels for transportation and synthetic chemicals is steam gasification of biomass in a dual fluid bed (DFB). The principle of this technology is the separation into a gasification and a combustion reactor. Bed material, nowadays olivine, circulates between them, and has two functions. It acts as a heat carrier from the combustion to the gasification zone and as catalyst regarding gasification reactions. Today, an alternative to olivine does yet not exist.In this work, experiments in a lab-scale test rig were performed investigating the catalytic activity of different fresh and used bed materials, such as olivine and quartz. The enhancement of the catalytic activity due to particle coatings was tested regarding the water-gas-shift reaction and steam reforming of toluene. Calcite is known as an active material in this respect and is therefore used as a benchmark substance.Experiments revealed a correlation between the catalytic activity of bed particle coatings towards both the water-gas-shift reaction and the reduction of toluene by steam reforming. Results showed bed material particles with a calcium (Ca)-rich layer achieve satisfactory conversion of carbon monoxide and reduction of toluene. Furthermore, a qualitative comparison regarding hydrogen production relative to the benchmark material CaO is given for the water-gas-shift and steam reforming of toluene and ethene - used as model substance for lighter hydrocarbons. These results are the basis for further research on the catalytic properties of potential bed materials for DFB gasification of biomass.     

Nickel catalyst auto-reduction during steam reforming of bio-oil model compound acetic acid

Transition metal catalysts widely used in refineries are provided as oxides and require pre-reduction to become activated. The auto-reduction of a NiO/Al₂O₃ catalyst with acetic acid (HAc) followed by HAc steam reforming was investigated in a packed bed reactor. Effects of temperature and molar steam to carbon ratio (S/C) on reduction kinetics and catalyst performance were analysed. Results showed that a steady steam reforming regime along with complete NiO reduction could be obtained after a coexistence stage of reduction and reforming. A 2D nucleation and nuclei growth model fitted the NiO auto-reduction. The maximum reduction rate constant was attained at S/C = 2. Steam reforming activity of the auto-reduced catalyst was just below that of the H₂-reduced catalyst, probably attributed to denser carbon filament formation and larger loss of active Ni. Despite this, a H₂ yield of 76.4% of the equilibrium value and HAc conversion of 88.97% were achieved at 750 °C and S/C = 3.     

Steam reforming of methanol,ethanol and glycerol over nickel-based catalysts-A review

Depletion of non-renewable energy sources such as coal and natural gas is paving the way to generate alternative energy sources. Hydrogen, a very promising alternative energy has the highest energy density (143 MJ/kg) compared to any known fuel and it has zero air pollution due to the formation of water as the only by-product after combustion. Currently, 95% of hydrogen is produced from non-renewable sources. Hydrogen production from renewable sources is considered a promising route for development of sustainable energy production. Steam reforming of renewable sources such as methanol, ethanol and glycerol is a promising route to hydrogen production. This review covers steam reforming of these three alcohols using Ni-based catalysts with different supports. Chemistry of the steam reforming reactions is discussed. Hydrogen yield depends on operating conditions, the nature of active metal and the catalyst support. Supports play an important role in terms of hydrogen selectivity and catalyst stability because of their basic characteristics and redox properties. Synthesis of suitable catalysts that can suppress coke formation during reforming is suggested.     

A review on anode on-cell catalyst reforming layer for direct methane solid oxide fuel cells

The commercialization of solid oxide fuel cells (SOFCs) can be significantly promoted with the direct utilization of methane, which is the primary component in natural gas and the second most abundant anthropogenic greenhouse gas. However, carbon deposition on most commonly used Ni-based anode is the bottle-necking issue inhibiting long-term stability of direct methane SOFCs. To avoid such a problem, methane is typically reformed (internally or externally) in SOFCs. Considering the cost, system simplification, coking resistance, and material selection, the on-cell catalytic reforming layer (OCRL) is one of the most promising designs for direct methane SOFCs. Reforming catalytic materials are typically consisted of active component, substrate and catalytic promoter, all of which have a significant impact on the catalytic activity, sintering resistance and coking resistance of methane reforming catalysts. This review summarizes the influence of the various components, some common OCRL materials and their applications in direct methane SOFCs, reforming and coking resistance mechanism, as well as the remaining challenges. The effective utilization of OCRL plays a pivotal role in promoting the development of direct methane SOFCs and the commercialization of SOFCs.     

Steam reforming of propionic acid: Thermodynamic analysis of a model compound for hydrogen production from bio-oil

The thermodynamic equilibrium of steam reforming of propionic acid (HPAc) as a bio-oil model compound was studied over a wide range of reaction conditions (T = 500–900 °C, P = 1–10 bar and H₂O/HPAc = 0–4 mol/mol) using non-stoichiometric equilibrium models. The effect of operating conditions on equilibrium conversion, product composition and coke formation was studied. The equilibrium calculations indicate nearly complete conversion of propionic acid under these conditions. Additionally, carbon and methane formation are unfavorable at high temperatures and high steam to carbon (S/C) ratios. The hydrogen yield versus S/C ratio passes a maximum, the value and position of which depends on temperature. The thermodynamic equilibrium results for HPAc fit favorably with experimental data for real bio-oil steam reforming under same reaction conditions.     

The intrinsic kinetics of methane steam reforming over a nickel-based catalyst in a micro fluidized bed reaction system

Methane steam reforming (MSR) is studied experimentally and numerically. The intrinsic kinetics of the reaction are determined using a micro fluidized bed with a catalyst containing more than 50 wt % NiO/α-Al₂O₃. Intrinsic kinetic models are developed for parallel and serial reaction mechanisms, but the parallel mechanism is found to better match the experimental data. The activation energies for CO and CO₂ formation are 81.69 kJ/mol and 59.38 kJ/mol, respectively, and the pre-exponential factors are 316.6 mol/(g h kPa^0.85) and 0.00263 mol/(g h kPa^3.1), respectively. As the reaction temperature increases, the rate of CO formation increases and that of CO₂ decreases. At 800 °C, almost all the CH₄ is converted to CO and H₂, and the methane conversion rate (X_CH4), the hydrogen production rate (Y_H2), and the CO selectivity (S_CO) are 92.28%, 3.34, and 0.99, respectively. The effects of the steam-to-carbon ratio (S/C), inlet velocity, and preheating temperature at different reaction temperatures are simulated using the FLUENT software package. As S/C increases, X_CH4 and Y_H2 increase, but S_CO decreases. The higher the reaction temperature, the less S/C promotes X_CH4 and Y_H2. When the reaction temperature is 700 °C and the inlet velocity is 0.2 m/s (residence time is 0.5 s), X_CH4 is above 95%, and changes in the inlet velocity strongly influence the formation of CO. With increasing preheating temperature, X_CH4, Y_H2, and S_CO all increase gradually.     

Catalytic and sorbent materials based on mayenite for sorption enhanced steam methane reforming with different packed-bed configurations

An experimental study was performed on sorption enhanced steam methane reforming (SESMR) by Ni-mayenite reforming catalyst and CaO-mayenite CO₂-sorbents with several CaO contents. Materials were synthesized, characterized (by XRD, BET and BJH methods, TPR) and tested in a micro-reactor, comparing two configurations: two separated, consequential packed-beds and the more usual raw mixing. Ni-mayenite always allowed a high, stable CH₄ conversion (>93%). A generalized direct effect from CO₂ capture emerged on water gas shift reaction extent, while enhancement of methane conversion took place only in raw mixing.In practical applications, investigated materials are bound to face alternatively reforming and sorbent regeneration conditions: an automated bench-scale system was used to perform 205 SESMR/regeneration cycles, with separate beds of Ni-mayenite and CaO-mayenite (30 wt% free-CaO), proving good activity and stability throughout cycles (stable CH₄ conversion > 95%, pre-breakthrough CO₂ concentration < 3 vol% dry, dilution-free).     

Catalytic performance of a high-cell-density Ni honeycomb catalyst for methane steam reforming

The catalysis of methane steam reforming (MSR) by pure Ni honeycombs with high cell density of 2300 cells per square inch (cpsi) was investigated to develop efficient and inexpensive catalysts for hydrogen production. The Ni honeycomb catalyst was assembled using 30-μm-thick Ni foils, and showed much higher activity than that of a Ni honeycomb catalyst with cell density of 700 cpsi at a steam-to-carbon ratio of 1.36 and a gas hourly space velocity of 6400 h^?1 in a temperature range of 873–1173 K. Notably, the activity increased approximately proportional to the increasing geometric specific surface area of the honeycombs. The turnover rate of the Ni honeycomb catalyst was higher than that of supported Ni catalysts. The changes in chemical state of the Ni catalyst during hydrogen reduction and MSR reaction were analyzed by in situ X-ray absorption fine structure spectroscopy, which revealed that deactivation was mainly due to oxidation of the surface Ni atoms. These results demonstrated that the high-cell-density Ni honeycomb catalyst exhibits good performance for MSR reaction, and easy regeneration of the deactivated Ni honeycomb catalyst is possible only via hydrogen reduction.     

Steam reforming of methane over Ni catalyst in micro-channel reactor

A comprehensive study on the catalytic performance of Ni catalyst to implement millisecond steam reforming of methane (SRM) reaction in micro-channel reactors was conducted in this work. A new method to manufacture the metal-ceramics complex substrate as catalyst support was presented, that is, a layer of nano-particles, α-Al₂O₃, was thermally sprayed on a metallic substrate, usually FeCrAlloy. Ni or Rh catalyst was then impregnated on the substrate, forming firm and active catalyst coatings. The fall-off rate of the catalyst can be neglected after the plates experienced the high-temperature SRM reaction, showing the reliability in long-term use and the excellent catalytic performance for SRM reaction in micro-channel reactors. In comparison with the expensive Rh catalyst, Ni also showed wonderful performance to catalyze the SRM reaction in micro-reactors within milliseconds. Using the appropriate reactor design, CH₄ conversion reached above 90% when the residence time was as short as 32 ms for catalyst loading of 6.8 g/m². When the residence time was longer than 100 ms, CH₄ conversion was above 98%. Besides, catalyst deactivation was not detected for 500 h on stream with S/C ratio of 3.0, and for 12 h with S/C of 1.0 as well. Extensive characterizations on these Ni catalyst plates using XRD, SEM, TEM and XPS demonstrated that Ni catalysts prepared in this work did not show any sign of deactivation after being used in the micro-channel system under high-temperature operation.     

Steam reforming of ethanol to hydrogen over nickel metal catalysts

In the present work acid‐treated Ni catalyst was investigated for the steam reforming (SR) of bio‐ethanol. Influential factors, such as reaction temperature, water‐to‐ethanol molar ratio and liquid hourly space velocity (LHSV), were investigated. The conversions were always complete at temperatures above 773 K, regardless of the changes of the reaction conditions. The yield to hydrogen increased with the increase in temperature and H₂O/C₂H₅OH molar ratios. The hydrogen yield up to 84% was reached under conditions: 923 K, LHSV of 5.0 ml g⁻¹ h⁻¹, H₂O/C₂H₅OH ratio of 10 over the acid‐treated Ni catalyst. The effects of the influential factors on the side reactions and the distribution of byproducts were discussed. Copyright © 2010 John Wiley & Sons, Ltd.     

Mechanistic insights into methanol steam reforming over a ZnZr oxide catalyst with improved activity

Methanol steam reforming (MSR) holds great potential for mobile hydrogen production, but it still requires an active and stable catalyst. In this work, we report a high-performance ZnZr-0.5 composite oxide catalyst for this reaction, with a hydrogen production rate of 2.80 mol·g_cat^?1·h^?1 and CO₂ selectivity of 99.6% at a methanol space velocity of 22,762 mL·g_cat^?1·h^?1. It also exhibits superior long-term durability in the TOS test for more than 100 h. Such good activity results from a synergistic effect of ZnO–ZrO₂ dual sites. ZrO₂ is capable of stabilizing and storing more CH₃O1 and HCOO1 intermediates while ZnO is in charge of the dehydrogenation of these key intermediates. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and chemisorption results reveal that the MSR reaction experiences successively the hydrolysis of methyl formate and dehydrogenation of formate. More importantly, it is found that H₂O significantly promotes the dehydrogenation of HCOO1 intermediate by directly participating in this reaction from pulse chemisorption experiments.