Promoting effect of the interaction between Ni and CeO2 on steam gasification of biomass

Catalytic performance of Ni/CeO₂/Al₂O₃ catalysts prepared by a co-impregnation method was higher than that of Ni/CeO₂/Al₂O₃ by a sequential impregnation method and Ni/Al₂O₃ in steam gasification of biomass in terms of the yield of coke and tar. Characterization by means of temperature programmed reduction suggests that the intimate interaction between Ni and CeO₂ on the Ni/CeO₂/Al₂O₃ by the co-impregnation method can be related to high performance in steam gasification of biomass.     

Development of Ni catalysts for tar removal by steam gasification of biomass

Catalytic performance of Ni/CeO₂/Al₂O₃ catalysts prepared by a co-impregnation and a sequential impregnation method in steam gasification of real biomass (cedar wood) was investigated. Especially, Ni/CeO₂/Al₂O₃ catalysts prepared by the co-impregnation method exhibited higher performance than Ni/Al₂O₃ and Ni/CeO₂/Al₂O₃ prepared by the sequential impregnation method, and the catalysts gave lower yields of coke and tar, and higher yields of gaseous products. The Ni/CeO₂/Al₂O₃ catalysts were characterized by thermogravimetric analysis, temperature-programmed reduction with H₂, transmission electron microscopy and extended X-ray absorption fine structure, and the results suggested that the interaction between Ni and CeO₂ became stronger by the co-impregnation method than that by sequential method. Judging from both results of catalytic performance and catalyst characterization, it is found that the intimate interaction between Ni and CeO₂ can play very important role on the steam gasification of biomass.     

V-promoted Ni/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst for synthetic natural gas (SNG) production: Catalyst preparation methodologies

The effect of preparation method on the catalytic performance of V-promoted Ni/Al₂O₃ catalysts for synthetic natural gas (SNG) production via CO methanation has been investigated. The Ni-V/Al₂O₃ catalysts were prepared by co-impregnation (CI) method, deposition precipitation (DP) method as well as two sequential impregnation (SI) methods with different impregnation sequence. Among the prepared catalysts, the one prepared by CI method exhibited the best catalytic performance due to its largest H₂ uptake and highest metallic Ni dispersion. In a 91h-lifetime test, this catalyst showed high stability at high temperature and weight hourly space velocity. This work demonstrates that the catalytic performance of the V-promoted Ni/Al₂O₃ catalysts can be improved by carefully controlling the preparation method/conditions.     

Experimental Study on Catalytic Biomass Gasification in a Bubbling Fluidized Bed

A bubbling fluidized‐bed gasification system was selected for catalytic steam gasification of rice straw with four Ni‐based catalysts, i.e., Ni/Al₂O₃, Ni/CeO₂, Ni/MnO₂, and Ni/MgO. The effect of temperature, steam/biomass ratio (S/B), and catalyst/biomass ratio (C/B) on the gas composition, char conversion, and hydrogen yield was evaluated. It was found that higher temperature and S/B promote hydrogen production and char conversion. The results also demonstrated that the catalytic activity of Ni/Al₂O₃ under different S/B values is better than those of the other catalysts. Regarding the catalyst activity, all four catalysts exhibited good performance in terms of tar removal and carbon conversion. However, the performance of Ni/Al₂O₃ was superior to that of the other three catalysts.     

Effect of CeO<Subscript>2</Subscript>-addition sequence on the performance of CeO<Subscript>2</Subscript>-modified Ni/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst in autothermal reforming of iso-octane

Two types of CeO₂-modified Ni/Al₂O₃ catalysts were prepared by a consecutive impregnation method with different sequences in the impregnation of Ni and CeO₂, and their performance in autothermal reforming (ATR) of isooctane was investigated. Catalysts prepared by adding CeO₂ prior to the addition of Ni, Ni/CeO₂-Al₂O₃, produced larger amounts of hydrogen than those obtained using catalysts prepared by adding the two components in an opposite sequence, Ni-CeO₂/Al₂O₃. The results of H₂ chemisorption and temperature-programmed reduction revealed that added CeO₂ increased the dispersion of the Ni species on Al₂O₃ and suppressed the formation of NiAl₂O₄ in the catalyst such that large amounts of Ni species were present as NiO, the active species for the ATR. The elemental and thermogravimetric analyses of deactivated catalysts indicated that Ni/CeO₂-Al₂O₃, which showed a longer lifetime than Ni-CeO₂/Al₂O₃, contained lesser amounts and different types of coke on the surface.     

Catalytic Steam Reforming of Propane over Ni/LaAlO<Subscript>3</Subscript> Catalysts: Influence of Preparation Methods and OSC on Activity and Stability

Abstract  

To develop an efficient catalyst for steam reforming of propane, Ni/LaAlO₃ catalysts were prepared by deposition precipitation, impregnation, and solvo-thermal methods, and characterized by XRD, BET, H₂-TPR, elemental analyses, and TEM. Ni/Al₂O₃ and Ni/CeO₂ catalysts were also synthesized by the solvo-thermal method for comparison. The Ni/LaAlO₃ catalysts exhibited better catalytic performance than both Ni/Al₂O₃ and Ni/CeO₂ catalysts, and activities with Ni/LaAlO₃ were found to be dependent upon the preparation methods. In particular, the Ni/LaAlO₃ catalyst synthesized by the solvo-thermal method exhibited the highest activity presumably because tetrahydrofuran helps distribute generated Ni nanoparticles onto the catalyst surface in a uniform fashion. In addition, the solvo-thermally prepared Ni/LaAlO₃ catalyst was found to be highly stable, with its activity being maintained at least during 100 h. The observed high stability is attributed to the excellent oxygen storage capacity of LaAlO₃, which was first determined by thermogravimetric methods as well as by soot oxidations in the presence of Al₂O₃, CeO₂, and LaAlO₃. Compared to the Ni/Al₂O₃ and Ni/CeO₂ catalysts, Ni/LaAlO₃ exhibited suppressed carbon formation even at lower S/C ratios due to the superior oxygen transport ability of the LaAlO₃ support.     

Production of hydrogen by steam reforming of bio-oil over Ni/Al2O3 catalysts: Effect of addition of promoter and preparation procedure

Catalytic steam reforming of bio-oil was investigated in a fixed bed tubular reactor for production of hydrogen. Two series of nickel/alumina (Ni/Al₂O₃) supported catalysts promoted with ruthenium (Ru) and magnesium (Mg) were prepared. Each catalyst of the first series (Ru–Ni/Al₂O₃) was prepared by co-impregnation of nickel and ruthenium on alumina. They were examined to investigate the effect of adding ruthenium on the performance of the catalysts for hydrogen production. The effect of the temperature, the most effective parameter in the steam reforming of bio-oil, on the activity of the catalysts was also investigated. Each catalyst of the second series (Ni–MgO/Al₂O₃) was prepared by consecutive impregnation using various preparation procedures. They were tested to determine the effect of adding magnesium as well as the effect of the preparation procedure on the outlet gas concentrations. It was shown that in both series, the catalysts were more efficient in hydrogen production as well as carbon conversion than Ni/Al₂O₃ catalysts. The highest hydrogen yield was 85% which was achieved over Ru–Ni/Al₂O₃ at 950 °C. It was also found that the effect of adding a small amount of ruthenium was superior to that of nickel on the yield of hydrogen when the nickel content was equal to or greater than 10.7%.     

Promoting effect of Pt addition to Ni/CeO2/Al2O3 catalyst for steam gasification of biomass

The modification of Ni/CeO₂/Al₂O₃ with Pt can make the activation by H₂ reduction unnecessary, and this indicates that the Pt/Ni/CeO₂/Al₂O₃ catalyst can be activated automatically by the compounds contained in tar. This can be explained by the enhancement of the Ni reducibility by the addition of Pt. The results of the temperature programmed reduction with H₂ also support this enhancement. Furthermore, the addition of 0.1% Pt to Ni/CeO₂/Al₂O₃ (4 wt% Ni, 30 wt% CeO₂) enhanced the performance in the steam gasification of biomass, compared to Ni/Al₂O₃ and Ni/CeO₂/Al₂O₃ in terms of low tar yield and high gas yield. This can be related to the Pt–Ni alloy formation indicated by the extended X-ray absorption fine structure analysis.     

Combined Steam and Carbon Dioxide Reforming of Methane on Ni/MgAl<Subscript>2</Subscript>O<Subscript>4</Subscript>: Effect of CeO<Subscript>2</Subscript> Promoter to Catalytic Performance

Abstract  

The catalytic performance during combined steam and carbon dioxide reforming of methane (SCR) was investigated on Ni/MgAl₂O₄ catalyst promoted with CeO₂. The SCR catalyst was prepared by co-impregnation method using nickel and cerium metal precursors on hydrotalcite-like MgAl₂O₄ support. In terms of catalytic activity and stability, CeO₂-promoted Ni/MgAl₂O₄ catalyst is superior to Ni–CeO₂/Al₂O₃ or Ni/MgAl₂O₄ catalysts because of high resistance to coke formation and suppressed aggregation of nickel particles. The role of CeO₂ on Ni/MgAl₂O₄ catalyst was elucidated by carrying out the various characterization methods in the viewpoint of the aggregation of nickel particles and metal-support interactions. The observed superior catalytic performance on CeO₂-promoted Ni/MgAl₂O₄ catalyst at the weight ratio of MgO/Al₂O₃ of 3/7 seems to be closely related to high dispersion and low aggregation of active metals due to their strong interaction with the MgAl₂O₄ support and the adjacent contact of Ni and CeO₂ species. The CeO₂ promoter also plays an important role to suppress particle aggregation by forming an appropriate interaction of NiO–CeO₂ as well as Ni–MgAl₂O₄ with the concomitant enhancement of mobile oxygen content.     

The effect of impregnation strategy on structural characters and CO2 methanation properties over MgO modified Ni/SiO2 catalysts

Mg-modified Ni/SiO₂ catalysts with different MgO contents were prepared by two impregnation methods. The catalysts prepared by co-impregnation method could show better activity and stability than those prepared by sequential impregnation method. The modification of MgO acted as a key factor in enhancing the capacity of CO₂ adsorption and accelerating the activation of CO₂. Moreover, modified MgO could also increase Ni species dispersion and suppress the metallic Ni sintering and oxidation.     

Hydrogen production by steam reforming of LNG over Ni/Al2O3-ZrO2 catalysts: Effect of ZrO2 and preparation method of Al2O3-ZrO2

An Al₂O₃-ZrO₂ support was prepared by grafting a zirconium precursor onto the surface of commercial γ-Al₂O₃. A physical mixture of Al₂O₃-ZrO₂ was also prepared for the purpose of comparison. Ni/Al₂O₃-ZrO₂ catalysts were then prepared by an impregnation method, and were applied to the hydrogen production by steam reforming of liquefied natural gas (LNG). The effect ZrO₂ and preparation method of Al₂O₃-ZrO₂ on the performance of supported nickel catalysts in the steam reforming of LNG was investigated. The Al₂O₃-ZrO₂ prepared by a grafting method was more efficient as a support for nickel catalyst than the physical mixture of Al₂O₃-ZrO₂ in the hydrogen production by steam reforming of LNG. The well-developed tetragonal phase of ZrO₂ and the high dispersion of ZrO₂ on the surface of γ-Al₂O₃ were responsible for the enhanced catalytic performance of Ni/Al₂O₃-ZrO₂ prepared by way of a grafting method.     

Effect of Catalyst Supports on Water‐Gas Shift Reaction at Ultrahigh Temperatures Using Syngas

Monometallic and bimetallic catalysts (Pt, Ni, and Pt‐Ni) with single support (Al₂O₃, TiO₂) and composite support (CeO₂/Al₂O₃, CeO₂/TiO₂) were prepared and tested for water‐gas shift reaction in a tubular quartz reactor. Syngas and steam with different steam‐to‐carbon ratios served as feedstock. The operating pressure was fixed while the reaction temperature was varied. The measured results indicated that the monometallic Ni/Al₂O₃ catalyst exhibits the lowest CO conversion and H₂ yield as compared with other catalysts. About the same CO conversion can be obtained from Pt and Pt‐Ni catalysts with single or composite support. However, higher H₂ yield can be achieved from the TiO₂‐supported catalyst compared with those supported by Al₂O₃. The experimental data also indicated that good thermal stability can be reached for the Pt‐based catalysts studied.     

Preparation and characterizations of Ni-alumina,Ni-ceria and Ni-alumina/ceria catalysts and their performance in biomass pyrolysis

The catalytic activity of Ni/Al₂O₃, Ni/CeO₂, and Ni/Al₂O₃-CeO₂ catalysts of different compositions were investigated over biomass pyrolysis process. Catalysts were prepared using co-precipitation method with various compositions of nickel and support materials. Surface characterizations of the materials were evaluated using XRD, SEM, and BET surface area analysis with N₂ adsorption isotherm. XRD analysis reveals the presence of Al₂O₃, CeO₂, NiO, and NiAl₂O₄ phases in the catalysts. Paper samples used for daily writing purposes were chosen as biomass source in pyrolysis. TGA experiment was performed on biomass with and without presence of catalysts, which resulted in the decrease of initial degradation temperature of paper biomass with the influence of catalysts. In a fixed-bed reactor, untreated and catalyst mixed biomasses were pyrolyzed up to 800 °C, with a residence time of 15 min. The non-condensable gases were collected through gas bags every after 100 °C and also at 5, 10, and 15 min residence time at 800 °C, which were analyzed using TCD-GC equipment. Comparative distributions of solid, liquid and gaseous components were made. Results indicated diminished amount of tar production in presence of catalysts. 30 wt% Ni/CeO₂ catalyst yielded least amount of tar product. The least amount of CO was produced over the same catalyst. According to gas analysis result, 30 wt% Ni doped alumina sample produced maximum amount of H₂ production with 43.5 vol% at 800 °C (15 min residence time).     

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.     

Effects of Ga doping on Pt/CeO2‐Al2O3 catalysts for propane dehydrogenation

This paper describes catalytic consequencesThis paper describes catalytic consequences of Pt/CeO₂‐Al₂O₃ catalysts promoted with Ga species for propane dehydrogenation. A series of PtGa/CeO₂‐Al₂O₃ catalysts were prepared by a sequential impregnation method. The as‐prepared catalysts were characterized employing N₂ adsorption‐desorption, X‐ray diffrtaction, temperature programmed reduction, O₂ volumetric chemisorption, H₂‐O₂ titration, and transmission electron microscopy. We have shown that Ga³⁺ cations are incorporated into the cubic fluorite structure of CeO₂, enhancing both lattice oxygen storage capacity and surface oxygen mobility. The enhanced reducibility of CeO₂ is indicative of higher capability to eliminate the coke deposition and thus is beneficial to the improvement of catalytic stability. Density functional theory calculations confirm that the addition of Ga is prone to improve propylene desorption and greatly suppress deep dehydrogenation and the following coke formation. The catalytic performance shows a strong dependence on the content of Ga addition. The optimal loading content of Ga is 3 wt %, which results in the maximal propylene selectivity together with the best catalytic stability against coke accumulation. © 2016 American Institute of Chemical Engineers AIChE J, 62: 4365–4376, 2016     

Effect of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-ZrO<Subscript>2</Subscript> xerogel support on hydrogen production by steam reforming of LNG over Ni/Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-ZrO<Subscript>2</Subscript> catalyst

An Al₂O₃-ZrO₂ xerogel (AZ-SG) was prepared by a sol-gel method for use as a support for a nickel catalyst. The Ni/AZ-SG catalyst was then prepared by an impregnation method, and was applied to hydrogen production by steam reforming of LNG. A nickel catalyst supported on commercial alumina (A-C) was also prepared (Ni/A-C) for comparison. The hydroxyl-rich surface of the AZ-SG support increased the dispersion of nickel species on the support during the calcination step. The formation of a surface nickel aluminate-like phase in the Ni/AZ-SG catalyst greatly enhanced the reducibility of the Ni/AZ-SG catalyst. The ZrO₂ in the AZ-SG support increased the adsorption of steam onto the support and the subsequent spillover of steam from the support to the active nickel sites in the Ni/AZ-SG catalyst. Both the high surface area and the well-developed mesoporosity of the Ni/AZ-SG catalyst improved the gasification of adsorbed surface hydrocarbons in the reaction. In the steam reforming of LNG, the Ni/AZ-SG catalyst showed a better catalytic performance than the Ni/A-C catalyst. Moreover, the Ni/AZ-SG catalyst showed strong resistance toward catalyst deactivation.     

Hydrogen production by steam gasification of polypropylene with various nickel catalysts

Several nickel-based catalysts (Ni/Al₂O₃, Ni/MgO, Ni/CeO₂, Ni/ZSM-5, Ni-Al, Ni-Mg-Al and Ni/CeO₂/Al₂O₃) have been prepared and investigated for their suitability for the production of hydrogen from the two-stage pyrolysis–gasification of polypropylene. Experiments were conducted at a pyrolysis temperature of 500 °C and gasification temperature was kept constant at 800 °C with a catalyst/polypropylene ratio of 0.5. Fresh and reacted catalysts were characterized using a variety of methods, including, thermogravimetric analysis, scanning electron microscopy with energy dispersive X-ray spectrometry and transmission electron microscopy. The results showed that Ni/Al₂O₃ was deactivated by two types of carbons (monoatomic carbons and filamentous carbons) with a total coke deposition of 11.2 wt.% after reaction, although it showed to be an effective catalyst for the production of hydrogen with a production of 26.7 wt.% of the theoretical yield of hydrogen from that available in the polypropylene. The Ni/MgO catalyst showed low catalytic activity for H₂ production, which might be due to the formation of monoatomic carbons on the surface of the catalyst, blocking the access of gaseous products to the catalyst. Ni-Al (1:2) and Ni-Mg-Al (1:1:2) catalysts prepared by co-precipitation showed good catalytic abilities in terms of both H₂ production and prevention of coke formation. The ZSM-5 zeolite with higher surface area was also shown to be a good support for the nickel-based catalyst, since, the Ni/ZSM-5 catalyst showed a high rate of hydrogen production (44.3 wt.% of theoretical) from the pyrolysis–gasification of polypropylene.     

Catalyst Design of Pt-Modified Ni/Al2O3 Catalyst with Flat Temperature Profile in Methane Reforming with CO2 and O2

Pt(0.3)/Ni(10)/Al₂O₃, prepared by a sequential impregnation method, exhibited a more excellent performance in methane reforming with CO₂ and O₂ in terms of the catalytic activity and the temperature profile of the catalyst bed than Pt(0.3) + Ni(10)/Al₂O₃ prepared by a coimpregnation method, Ni(10)/Al₂O₃, Pt(0.3)/Al₂O₃, and Pt(10)/Al₂O₃. It is thought that this is because the surface Pt atoms on Ni catalyst can contribute to the enhancement of the catalyst reducibility.     

Catalytic performance and QXAFS analysis of Ni catalysts modified with Pd for oxidative steam reforming of methane

Pd–Ni bimetallic catalysts prepared by co-impregnation and sequential impregnation methods were compared in the catalytic performance in oxidative steam reforming of methane. The sequential impregnation was more effective to the suppression of hot spot formation. According to the structural analysis by in situ quick-scanning X-ray absorption fine structure (QXAFS) during the temperature programmed reduction, the sequential impregnation method gave the bimetallic particles with higher Pd surface composition because of the low possibility of the Pd–Ni bond formation. Higher surface composition of Pd with higher reducibility than Ni is connected to the enhancement of the catalyst reducibility and the suppression of the hot spot formation.     

Thin‐Film Catalytic Coating of a Microreactor for Preferential CO Oxidation over Pt Catalysts

Different Pt‐based catalyst layers have been prepared and tested in a stacked foil microreactor for CO oxidation and preferential oxidation of CO in presence of hydrogen. The reactions were performed on Pt without support by impregnation of a pre‐oxidized microstructured metal plate, Pt/Al₂O₃ and Pt/CeO₂ based on sol methods as well as Pt/nano‐Al₂O₃, a combined method of sol‐gel and nanoparticle slurry coating. The ceria based sol‐gel catalyst was much more active for CO oxidation than alumina based sol‐gel catalysts at low temperature. However, total oxidation was only obtained at higher temperature on the alumina based catalysts. The combined method seems to have advantages in terms of less internal mass transfer limitation when trying to increase the catalyst coating thickness based on sol‐gel approaches due to no reduction of CO selectivity up to 300 °C reaction temperature. Experiments on CO oxidation with the Pt/CeO₂ catalyst have been conducted in an oxygen supply microreactor to evaluate the catalyst performance under sequential oxygen supply to reaction zone (CO excess).