Catalytic decomposition of biomass tars with iron oxide catalysts

Catalytic gasification of wood (Cedar) biomass was carried out using a specially designed flow-type double beds micro reactor in a two step process: temperature programmed non-catalytic steam gasification of biomass was performed in the first (top) bed at 200–850 °C followed by catalytic decomposition gasification of volatile matters (including tars) in the second (bottom) bed at a constant temperature, mainly 600 °C. Iron oxide catalysts, which transformed to Fe₃O₄ after use possessed catalytic activity in biomass tar decomposition. Above 90% of the volatile matters was gasified by the use of iron oxide catalyst (prepared from FeCl₃ and NH_3aq) at SV of 4.5 × 10³ h^?1. Tar was decomposed over the iron oxide catalysts followed by water gas shift reaction. Surface area of the iron oxide seemed to be an important factor for the catalytic tar decomposition. The activity of the iron oxide catalysts for tar decomposition seemed stable with cyclic use but the activity of the catalysts for the water gas shift reaction decreased with repeated use.     

Catalytic steam reforming of biomass-derived tar for hydrogen production with K2CO3/NiO/γ-Al2O3 catalyst

A major problem of using Ni-based catalysts is deactivation during catalytic cracking and reforming, lowering catalytic performance of the catalysts. Modification of catalyst with alkali-loading was expected to help reduce coke formation, which is a cause of the deactivation. This paper investigated the effects of alkali-loading to aluminasupported Ni catalyst on catalytic performance in steam reforming of biomass-derived tar. Rice husk and K₂CO₃ were employed as the biomass feedstock and the alkali, respectively. The catalysts were prepared by a wet impregnation method with γ-Al₂O₃ as a support. A drop-tube fixed bed reactor was used to produce tar from biomass in a pyrolysis zone incorporated with a steam reforming zone. The result indicated that K₂CO₃/NiO/γ-Al₂O₃ is more efficient for steam reforming of tar released from rice husk than NiO/γ-Al₂O₃ in terms of carbon conversion and particularly hydrogen production. Effects of reaction temperature and steam concentration were examined. The optimum temperature was found to be approximately 1,073 K. An increase in steam concentration contributed to more tar reduction. In addition, the K₂CO₃-promoted NiO/γ-Al₂O₃ was found to have superior stability due to lower catalyst deactivation.     

Development of new nickel based catalyst for tar reforming with superior resistance to sulfur poisoning and coking in biomass gasification

Gasification of tar by catalytic steam reforming was examined in the gasification process of biomass, such as dried sewage sludge and wood chips. The tar reforming characteristics of the newly-developed Ni/MgO–CaO (based on dolomite) catalyst which was doped with WO₃ as a sulfur-resistant promoter, was investigated using a simulated gas containing naphthalene as tar. The result has confirmed that the developed catalyst shows a high naphthalene reforming activity and is stable even in gas containing hydrogen sulfide. The catalyst also exhibited superior resistance to coking as well as sulfur poisoning compared to several commercial steam-reforming catalysts.     

Catalytic reforming of tar during gasification. Part II. Char as a catalyst or as a catalyst support for tar reforming

Char, char-supported catalysts and ilmenite were investigated for the steam reforming of biomass tar derived from the pyrolysis of mallee wood in situ. Special attention was given to the reforming of aromatic ring systems in tar. The results indicated that the char-supported iron/nickel catalysts exhibited much higher activity for the reforming of tar than the char itself. Ilmenite and the char-supported iron catalyst contained similar active phase but showed different tar reforming activities. Kinetic compensation effects demonstrated that the reaction pathways on the char-supported catalysts were similar but were different from those on ilmenite. The proprieties of support could play important roles for the activities of the catalysts and the reaction pathways on the catalysts. Char would not only disperse the catalysts but also interact with the catalysts to enhance their activity for the steam reforming of tar.     

Catalytic activity of coal ash on steam methane reforming and water-gas shift reactions

The catalytic activity of Clarion 4A coal ash on water-gas shift, steam methane reforming and carbon dioxide methane reforming reactions was studied in an atmospheric fluidized bed over temperatures ranging from 370°C to 900°C. The rates of steam methane reforming and water-gas shift reactions over ash were found to be several times the corresponding non-catalytic reactions but were one order of magnitude lower than the reactions over commercial catalysts. Also, it was found that the ash affected the water-gas shift reaction more significantly than the steam methane reforming reaction probably because of the larger amount of iron oxide in the coal ash. However, there was no appreciable reaction for carbon dioxide reforming up to 900°C.     

Catalytic reforming of tar during gasification. Part I. Steam reforming of biomass tar using ilmenite as a catalyst

Ilmenite, a natural iron-containing mineral, has been investigated as an inexpensive catalyst for the steam reforming of volatiles (tar) from the pyrolysis of mallee woody biomass. The results indicate that ilmenite has good activity for the steam reforming of tar into gases due to its highly dispersed iron-containing species. The supply of external steam, in addition to the H₂O and CO₂ produced during the pyrolysis of biomass, plays an important role in minimising the formation of coke on the catalyst surface and thus the catalyst activity. The catalyst deactivation due to coke formation has more adverse effects on the reforming of larger aromatic ring system with steam than that of smaller ones. In addition, the supply of additional oxygen at low concentration changed the outcomes of tar reforming mainly because oxygen activated the smaller aromatic ring systems and polymerised them into larger aromatic ring systems in the gas phase.     

Bench- and Pilot-Scale Studies of Reaction and Regeneration of Ni–Mg–K/Al2O3 for Catalytic Conditioning of Biomass-Derived Syngas

The National Renewable Energy Laboratory (NREL) is collaborating with both industrial and academic partners to develop technologies to help enable commercialization of biofuels produced from lignocellulosic biomass feedstocks. The focus of this paper is to report how various operating processes, utilized in-house and by collaborators, influence the catalytic activity during conditioning of biomass-derived syngas. Efficient cleaning and conditioning of biomass-derived syngas for use in fuel synthesis continues to be a significant technical barrier to commercialization. Multifunctional, fluidizable catalysts are being developed to reform undesired tars and light hydrocarbons, especially methane, to additional syngas, which can improve utilization of biomass carbon. This approach also eliminates both the need for downstream methane reforming and the production of an aqueous waste stream from tar scrubbing. This work was conducted with NiMgK/Al₂O₃ catalysts. These catalysts were assessed for methane reforming performance in (i) fixed-bed, bench-scale tests with model syngas simulating that produced by oak gasification, and in pilot-scale, (ii) fluidized tests with actual oak-derived syngas, and (iii) recirculating/regenerating tests using model syngas. Bench-scale tests showed that the catalyst could be completely regenerated over several reforming reaction cycles. Pilot-scale tests using raw syngas showed that the catalyst lost activity from cycle to cycle when it was regenerated, though it was shown that bench-scale regeneration by steam oxidation and H₂ reduction did not cause this deactivation. Characterization by TPR indicates that the loss of a low temperature nickel oxide reduction feature is related to the catalyst deactivation, which is ascribed to nickel being incorporated into a spinel nickel aluminate that is not reduced with the given activation protocol. Results for 100?h time-on-stream using a recirculating/regenerating reactor suggest that this type of process could be employed to keep a high level of steady-state reforming activity, without permanent deactivation of the catalyst. Additionally, the differences in catalyst performance using a simulated and real, biomass-derived syngas stream indicate that there are components present in the real stream that are not adequately modeled in the syngas stream. Heavy tars and polycyclic aromatics are known to be present in real syngas, and the use of benzene and naphthalene as surrogates may be insufficient. In addition, some inorganics found in biomass, which become concentrated in the ash following biomass gasification, may be transported to the reforming reactor where they can interact with catalysts. Therefore, in order to gain more representative results for how a catalyst would perform on an industrially-relevant scale, with real contaminants, appropriate small-scale biomass solids feeders or slip-streams of real process gas should be employed.     

Hydrogen Sulfide-Resistant Bifunctional Catalysts for the Steam Reforming of Methane: Activity and Structural Evolution

Results are presented from studying an iron–nickel catalyst for the steam reforming of methane, synthesized by epitaxial coating on the surface of spherical pellets of commercial γ-Al₂O₃. It is shown the catalyst is resistant to the presence of hydrogen sulfide in a steam–gas mixture. The degree of conversion of methane during reforming is close to equilibrium at a pressure of 2.0 MPa, a temperature of 800°C, a ratio of Н₂О: СН4 = 2: 1, a feedstock hourly space velocity (FHSV) of 6000 h^?1, and a H₂S concentration of 30 ppm. The structural evolution and phase state of the active components of the system are studied via X-ray diffraction analysis, transmission electron microscopy (TEM), and Mössbauer spectroscopy. The formation of paramagnetic iron oxide clusters tightly bound to the structure of the support, and of FeNi₃ iron–nickel alloy particles on the surface of the catalyst, is responsible for the polyfunctional properties of the catalyst, which displays high activity in both the steam reforming of methane and the oxidative decomposition of hydrogen sulfide to elemental sulfur.     

Steam reforming model compounds of biomass gasification tars: conversion at different operating conditions and tendency towards coke formation

The purification of biomass-derived syngas via tar abatement by catalytic steam reforming has been investigated using benzene, toluene, naphthalene, anthracene and pyrene as surrogated molecules. The effects of temperature and steam-to-carbon ratio on conversion, and the tendency towards coke formation were explored for each model compound. Two commercial nickel-based catalysts, the UCI G90-C and the ICI 46-1, were evaluated. The five tar model compounds had very different reaction rates. Naphthalene was the most difficult compound to steam reform, with conversions from 0.008 g_{org_conv}/g_cat min (790 °C) to 0.022 g_{org_conv}/g_cat min (890 °C) at an S/C ratio of 4.2. The most reactive compound was benzene, with a conversion of 1.1 g_{org_conv}/g_cat min at 780 °C and an S/C ratio of 4.3. The tendency towards coke formation grew as the molecular weight of the aromatic increased. The minimum S/C ratio for toluene was 2.5 at a catalyst temperature of 725 °C, and for pyrene at 790 °C ,it was 8.4. In general, catalyst temperatures and S/C ratios need to be higher than for naphtha in order to prevent the formation of coke on the catalyst.     

Hydrogen Production by Steam Reforming of Liquefied Natural Gas Over Mesoporous Ni-Al2O3 Composite Catalyst Prepared by a Single-step Non-ionic Surfactant-templating Method

A mesoporous Ni-Al₂O₃ composite catalyst (Ni-A-NS) was prepared by a single-step non-ionic surfactant-templating method for use in hydrogen production by steam reforming of liquefied natural gas (LNG). For comparison, a nickel catalyst supported on mesoporous alumina (Ni/A-NS) was also prepared by an impregnation method. The effect of physicochemical properties on the performance of Ni-A-NS catalyst in the steam reforming of LNG was investigated. Ni-A-NS catalyst retained superior textural properties compared to Ni/A-NS catalyst. Nickel oxide species were highly dispersed on the surface of both Ni/A-NS and Ni-A-NS catalysts through the formation of surface nickel aluminate phase. Although both Ni/A-NS and Ni-A-NS catalysts exhibited a stable catalytic performance, Ni-A-NS catalyst showed a better catalytic performance than Ni/A-NS catalyst in the steam reforming of LNG. High nickel surface area and high nickel dispersion of Ni-A-NS catalyst played an important role in enhancing the dehydrogenation reaction of hydrocarbon species and the gasification reaction of adsorbed carbon species in the steam reforming of LNG. High reducibility of Ni-A-NS catalyst was also responsible for its high catalytic performance.     

Characterization and oxidation states of Cu and Pd in Pd–CuO/ZnO/ZrO2 catalysts for hydrogen production by methanol partial oxidation

Copper and zinc oxide based catalysts prepared by coprecipitation were promoted with palladium and ZrO₂, and their activity and selectivity for methanol oxidative reforming was measured and characterized by N₂O decomposition, X-ray absorption spectroscopy, BET, X-ray photoelectron spectroscopy, X-ray diffraction, and temperature programmed reduction. Addition of ZrO₂ increased copper dispersion and surface area, with little effect on activity, while palladium promotion significantly enhanced activity with little change of the catalytic structure. A catalyst promoted with both ZrO₂ and palladium yielded hydrogen below 150 °C. EXAFS results under reaction conditions showed that the oxidation state of copper was influenced by palladium in the catalyst bulk. A palladium promoted catalyst contained 90% Cu⁰, while the copper in an unpromoted catalyst was 100% Cu¹⁺ at the same temperature. Palladium preferentially forms an unstable alloy with copper instead of zinc during reduction, which persists during reaction regardless of copper oxidation state. A 100-h time on stream activity measurement showed growth in copper crystallites and change in copper oxidation state resulting in decreasing activity and selectivity. A kinetic model of the reaction pathway showed that palladium and ZrO₂ promoters lower the activation energy of methanol combustion and steam reforming reactions.     

Development of new nickel based catalyst for biomass tar steam reforming producing H2-rich syngas

Mayenite (Ca₁₂Al₁₄O₃₃ or 12CaO.7Al₂O₃) was previously developed and applied as Ni support for biomass tar steam reforming in the absence and presence of H₂S by our group because of its high oxygen restoring property in the structure [C. Li et al., Appl. Catal., B. 2008]. In this study, catalyst Ni/mayenite (mayenite as support) was prepared by impregnation method with nickel nitrate hexahydrate. Experiments were tested in a fixed-bed reactor, toluene as a tar model compound. The influence of the catalyst preparation and operating parameters (reaction temperature, steam to carbon ratio and space time) on catalyst activity and products selectivity were studied, and a long-time evaluation (more than 76 h) also exhibited excellent resistance to coking. These results were compared to these obtained by commercial-like catalysts: Ni/CaO_x/MgO_1−x and our previous NiO/mayenite, showing that Ni/mayenite exhibited excellent property for biomass tar reforming, with higher H₂ yield than that of Ni/CaO_x/MgO_1−x, and higher CO selectivity than that of NiO/mayenite. For kinetic model, the first order reaction used for toluene with activation energy of 80.24 kJ.mol^− 1 was coincident with literature data.     

Steam reforming of tar from a biomass gasification process over Ni/olivine catalyst using toluene as a model compound

A Ni/olivine catalyst, previously developed for biomass gasification and tar removal during fluidized bed steam gasification of biomass, was tested in a fixed bed reactor in toluene steam reforming as a tar destruction model reaction. The influence of the catalyst preparation parameters (nickel precursor, calcination temperature and nickel content) and operating parameters (reaction temperature, steam to carbon S/C ratio and space-time) on activity and selectivity was examined showing a high toluene conversion and a low carbon formation compared to olivine alone. The steam reforming of toluene was found to be of zero order for water and first order for toluene. Activation energy required for Ni/olivine was determined to be about 196 kJ mol⁻¹ in accordance with literature. Catalyst activity and stability and its resistance against carbon formation were discussed on the basis of X-ray diffraction (XRD), transmission electron microscopy (TEM) and temperature programmed oxidation (TPO) results. Characterization before test (XRD, temperature programmed reduction (TPR), Mössbauer spectroscopy) have shown the presence of NiO–MgO solid solution, formed on the surface of olivine support, which explains the efficiency of the catalyst calcined at 1100 °C. After test, Ni–Fe alloys were observed (TEM, Mössbauer spectroscopy). It was suggested that magnesium oxide enhanced steam adsorption, facilitating the gasification of surface carbon and that Ni–Fe alloys prevented carbon deposition by dilution effect.     

Pretreated olivine as tar removal catalyst for biomass gasifiers: investigation using naphthalene as model biomass tar

Biomass is considered as a potential source of renewable energy. One of the major problems for biomass gasification is the presence of tar in the product gas. We are investigating catalytic behaviour of olivine as a prospective bed additive for biomass gasifiers for tar removal. In the present paper, the pretreatment of olivine is investigated to improve its activity. Pretreatment method includes heating olivine at 900 °C in the presence of air for different treatment times. The catalytic activity of olivine is investigated via steam-reforming reaction of naphthalene as model biomass tar compound. Improvement in naphthalene conversion of around 30% is observed with 1 h of pretreatment. Also effect of pretreatment time is investigated. With increasing pretreatment time, conversion increases; more than 80% naphthalene conversion is observed with 10 h of pretreatment time for olivine. Both steam and dry reforming reaction of naphthalene forms more than 50% gaseous products over 10 h pretreated olivine. Besides the gaseous products and light tars, polymerization reactions occur producing higher tars in small quantity. Naphthalene conversion under syngas mixture is somewhat lower than that of only in steam and CO₂. Apparent activation energy of 187 kJ mol⁻¹ is determined for 10 h pretreated olivine under gasification-gas mixture.     

Stable Hydrogen Production from Ethanol through Steam Reforming Reaction over Nickel-Containing Smectite-Derived Catalyst

Hydrogen production through steam reforming of ethanol was investigated with conventional supported nickel catalysts and a Ni-containing smectite-derived catalyst. The former is initially active, but significant catalyst deactivation occurs during the reaction due to carbon deposition. Side reactions of the decomposition of CO and CH₄ are the main reason for the catalyst deactivation, and these reactions can relatively be suppressed by the use of the Ni-containing smectite. The Ni-containing smectite-derived catalyst contains, after H₂ reduction, stable and active Ni nanocrystallites, and as a result, it shows a stable and high catalytic performance for the steam reforming of ethanol, producing H₂.     

The effect of steam on pyrolysis and char reactions behavior during rice straw gasification

Steam gasification of biomass can generate hydrogen-rich, medium heating value gas. We investigated pyrolysis and char reaction behavior during biomass gasification in detail to clarify the effect of steam presence. Rice straw was gasified in a laboratory scale, batch-type gasification reactor. Time-series data for the yields and compositions of gas, tar and char were examined under inert and steam atmosphere at the temperature range of 873-1173 K. Obtained experimental results were categorized into those of pyrolysis stage and char reaction stage. At the pyrolysis stage, low H₂, CO and aromatic tar yields were observed under steam atmosphere while total tar yield increased by steam. This result can be interpreted as the dominant, but incomplete steam reforming reactions of primary tar under steam atmosphere. During the char reaction stage, only H₂ and CO₂ were detected, which were originated from carbonization of char and char gasification with steam (C + H₂O→CO + H₂). It implies the catalytic effect of char on the water-gas shift reaction. Acceleration of char carbonization by steam was implied by faster hydrogen loss from solid residue.     

Investigation of alumina-supported Ni and Ni-Pd catalysts by partial oxidation and steam reforming of n-octane

Aseries of nickel and nickel-palladium supported upon alumina catalysts were prepared in order to obtain a suitable catalyst that could be used in the process of producing hydrogen by partial oxidation and steam reforming of n-octane. Hydrogen production by partial oxidation and steam reforming (POSR) of n-octane was investigated over alumina-supported Ni and Ni-Pd catalysts. The process occurred by a combination of exothermic partial oxidation and endothermic steam reforming of n-octane. It was found that Ni/Al₂O₃ catalyst activity was high at high temperatures and increased with the Ni loadings. Its activity, however, was not obviously increased when Ni loadings were over 5.0 wt%. Compared with nickel catalyst, the bimetallic catalyst of Ni-Pd/A1₂O₃ showed markedly increased activity and hydrogen selectivity at experimental conditions. The catalytic performance also became more stable when the palladium was added, which indicated that palladium plays an essential role in the catalytic action. The used catalysts of Ni-Pd/A1₂O₃ were regenerated three times by using air at space velocity of 2,000 h⁻¹ to obtain a long duration catalyst. Also, the typical catalyst was characterized by using SEM, BET, TG and ICP methods in detail.     

Optimum operating conditions for a two-stage gasification process fueled by polypropylene by means of continuous reactor over ruthenium catalyst

We studied fuel gas production by means of pyrolysis and steam reforming of waste plastics for applications in solid oxide fuel cells. More specifically, we evaluated the effects of pyrolytic gasification temperature, catalyst content, steam reforming temperature, and weight hourly space velocity for a Ru catalyst used in a 60 g h^− 1-scale continuous experimental apparatus, which consisted of a tank reactor for pyrolysis and a packed-bed catalytic reactor for steam reforming. Polypropylene (PP) pellets were used as a model waste plastic. Ru/γ-Al₂O₃ catalysts with two different Ru contents were investigated. To suppress residue formation, the optimum operating temperature of the pyrolyzer was 673 K. To ensure suppressed coke formation, sufficient carbon conversion to gaseous products, and minimized heat loss from the reactor, the optimum operating conditions for the reformer were determined to be 903 K and 0.11 g-sample g-catalyst^− 1 h^− 1 with a 5 wt.% Ru/γ-Al₂O₃ catalyst. The composition of the gas produced with the 5 wt.% catalyst was almost the same as that predicted by chemical equilibrium laws, and it was applicable for a direct hydrocarbon fuel cell.     

High Surface Area CuMn2O4 Prepared by Silica-Aquagel Confined co-precipitation. Characterization and Testing in Steam Reforming of Methanol (SRM)

High surface area CuMn₂O₄ and mixtures of CuO and Mn₂O₃ were prepared via a novel template technique based on the coagulation—precipitation processes that occur when the metallic cations of salts dissolved in a silica aquagel medium are forced to precipitate by basic reagents. The oxides prepared by this method were tested as catalysts for the methanol steam reforming reaction at 250 °C and a very high space velocity (WHSV = 27.2 h⁻¹). CuMn₂O₄ with a high surface area (300 m²/g) and a tangled structure that apparently resembles the internal surface of the amorphous silica gel was obtained. The catalytic activity of this material is similar to that of the most active catalyst reported in the literature, with the advantage that its stability is enhanced. Contrary to what has been reported for low surface area particles, the physical mixture of copper oxide and manganese oxide nanoparticles prepared by the confined co-precipitation technique displayed a much lower catalytic activity than the spinel.     

Distribution of alkaline promoters within the structure of iron oxide catalyst for dehydrogenation

Along with potassium, cesium is an efficient promoter of catalytic activity of iron oxide catalysts for dehydrogenation of olefins and alkylaromatic hydrocarbons. In the reaction medium, a catalyst is a ferrite system consisting of potassium β″-polyferrite, potassium and cesium monoferrites, and magnetite. The character of the distribution of alkaline promoters within the catalyst structure is studied to provide the theoretically substantiated calculation of the optimal composition of this type of catalysts. The preferred location of cesium ions is shown to be the structure of β″-polyferrite of K_{2 ? z} Cs _z Fe²⁺Fe ₁₀ ³⁺ O₁₇ composition. The catalytic activity of this system with different contents of cesium in the dehydrogenation of ethylbenzene to styrene (flow-type reactor; 0.1 MPa; 600°C; hourly space velocity of ethylbenzene, 1 h^?1; ethylbenzene : steam weight ratio, 1 : 3) was tested. The maximum specific rate of styrene formation is attained at a Cs : Fe ratio in the interval 0.023–0.027, corresponding to the coefficient z = 0.26–0.30. It is impractical to introduce more cesium. Theoretical propositions for targeted transporting of a promoting agent to a given phase of a catalytically active ferrite system are developed. The content of expensive cesium compounds in iron oxide catalyst is optimized.