La-promoted Ni/γ-Al2O3 catalyst for autothermal reforming of methane

Autothermal reforming (ATR) of methane over the synthesized catalysts of 10Ni-2La/γ-Al₂O₃, 10Ni-2Ce/γ-Al₂O₃, 10Ni-2Co/γ-Al₂O₃ was investigated in the temperature range of 600-800 oC for the hydrogen production. The sequence of 2 wt% metal loading on nickel alumina support in relation to their catalytic performance was observed as La>Ce>Co. The excellent activity and selectivity of 10Ni-2La/γ-Al₂O₃ was superior to other catalysts owing to little carbon deposition (~2.23 mg coke/gcath), high surface area and good dispersion and stability in the alumina support. The reforming of methane was inferred to be initiated by the decomposition of hydrocarbon at the inlet zone, preceded by the reforming reactions in the catalyst bed. Our result shows that it can be possible to achieve the H₂/CO ratio optimal to the GTL processes by controlling the O₂/CH₄ ratio of the feed inlet. The addition of oxygen to the feed inlet enhanced conversion efficiency substantially; probably, it favors the re-oxidation of carbonaceous residues formed over the catalyst surfaces, avoiding the catalyst deactivation and hence promoting catalyst stability.     

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.     

Glycerol steam reforming over Ni/γ-Al2O3 catalysts modified by metal oxides

The metal oxides modified Ni/γ-Al₂O₃ catalysts for glycerol steam reforming were prepared by impregnation. Characterization results of fresh catalysts indicated that the molybdates modification abated the acidity and the stronger metal-support interaction of Ni/γ-Al₂O₃ catalysts, leading to a stable catalytic activity. Especially, NiMoLa-CaMg/γ-Al₂O₃ (NiMoLa/CMA) catalyst exhibited no deactivation along with glycerol complete conversion to stable gaseous products containing 69% H₂, 20% CO and 10% CO₂ during time-on-stream of 42 h. TPO of spent Ni/γ-Al₂O₃ catalysts modified by different components showed that the carbon deposit on acidic sites and NiAl₂O₄ species led to catalysts deactivation. A lower reforming temperature and a higher LHSV and glycerol content were helpful to the production of syngas from GSR over NiMoLa/CMA; the reverse conditions would improve the formation of H₂.     

Role of support in CO2 reforming of CH4 over a Ni/γ-Al2O3 catalyst

A catalyst of 10% Ni/γ-Al₂O₃ for CO₂/CH₄ reforming was prepared and characterized by TPR, TPD, XPS, XRD and activity measurements. XPS and TPR showed that Ni mainly exists in the form of NiAl₂O₄ in the calcined catalyst and is hard to reduce below 650°C, indicating a strong interaction between metal and support. Reduction of the calcined catalyst results in fine particles of Ni⁰, with an average diameter of about 20 nm as determined by XRD. The uptake of H on the reduced catalyst measured by H₂-TPD is 4.2–4.6 mole per mole of Ni species and does not depend on the reduction degree of Ni species. This provides a convincing piece of evidence for the occurrence of hydrogen spillover in the reduced catalyst. Only reduced catalysts present good activity, but the degree of nickel reduction has almost no effect on the reforming activity. This seems to suggest that Ni⁰ is vital for the reforming activity, but γ-Al₂O₃ is also involved in CO₂/CH₄ reforming and contributes even more. Based on the mechanism proposed by Bradford et al. and on our observations, a mechanistic model has been proposed to elucidate the role of γ-Al₂O₃ in CO₂/CH₄ reforming.     

NiMoNx/γ-Al2O3 catalyst for HDN of pyridine

A series of NiMoN_x/γ-Al₂O₃ catalysts with various Ni contents were prepared by a topotactic reaction between their corresponding precursors NiO·MoO₃/γ-Al₂O₃ and NH₃. The catalysts were characterized using BET, XRD, and H₂-TPR techniques, and the HDN activity of pyridine over these catalysts was tested. XRD patterns show that metallic Ni, Mo₂N and a new phase of Ni₃Mo₃N exist in NiMoN_x/γ-Al₂O₃ catalyst. H₂-TPR studies indicate that the presence of Ni lowers the reduction temperature of the passivated surface layer of nitrided Mo/γ-Al₂O₃. The HDN activity for NiMoN_x/γ-Al₂O₃ is much higher than that for NiMoS_x/γ-Al₂O₃. The nitride catalyst with about 5.0 wt% NiO and 15.0 wt% MoO₃ in its precursor has the highest specific denitrogenation activity. The appearance of Ni₃Mo₃N and the synergy between metallic Ni and nitrided Mo are probably responsible for the high activity of NiMoN_x/γ-Al₂O₃ catalyst. The role of Ni in HDN reaction was also investigated. The activities decrease in the order: reduced Ni/γ-Al₂O₃≥nitrided Ni/γ-Al₂O₃>partially reduced Ni/γ-Al₂O₃ and sulfided Ni/γ-Al₂O₃.     

The possibility of supercritical fluid regeneration for Pt-Re/γ-Al2O3 industrial reforming catalyst in O3/CO2 mixtures

This work continues a cycle of studies aimed at developing new approaches to the regeneration of coked bimetallic heterogeneous catalysts. The activities of three Ru-125 (Pt-Re/γ-Al₂O₃) industrial reforming catalyst samples (fresh catalyst (A), catalyst removed from an industrial reactor (B), and sample B after treating it with ozone in supercritical carbon dioxide (SC-CO₂) (C)) are been compared in the reforming of n-heptane. It is established that sample B is deactivated appreciably: the conversion of n-heptane and the yield of reforming products are generally much lower than on the fresh catalyst. After treating it with an O₃/SC-CO₂ mixture, the conversion of n-heptane not only returns to the level of fresh sample A, but also exceeds it by a factor of 1.2. The qualitative composition of the products obtained on samples A, B, and C is nearly the same, but there are some changes in the quantitative ratio of certain products. Regeneration with ozone is found to be promising for further development and scaling.     

Performance of Ni/MgO–AN catalyst in high pressure CO2 reforming of methane

The catalytic activity of 8.8 wt Ni/MgO–AN prepared from alcogel derived MgO was studied for the dry reforming of methane under high pressure (1.5 MPa). The catalyst showed a self-stabilization process during the reaction that lasted for 50 h, in which the catalytic activity decreased with increasing the reaction time on stream (TOS) up to 12 h, and then became stabilized thereafter. The activity decline during the initial 12 h of the reaction was found closely related to an increase in the amount of carbon deposits on the catalyst, which also became stabilized after the catalyst had served the reaction for 12 h. Comprehensive characterizations of the coked catalyst with Temprature programmed hydrogenation (TPH), X-ray photoelectron spectroscopy (XPS) and X-ray diffractometer (XRD) techniques revealed two kinds of carbon deposits (-carbon and -carbon) on the used catalyst. The -carbon deposits were found to be produced from CH4 decomposition while the -carbon deposits from CO disproportionation. It was revealed that the accumulation of -carbon deposits was a key cause for the activity decline and the self-stabilized catalysis during the initial 12 h of the high-pressure reaction. Moreover, it was also observed that an unavoidable sintering of metallic Ni particles from 6.5 to 11 nm, which happened within the very first hour of the reaction, was not directly related to the catalyst stability.     

Hydrogen production by sorption-enhanced steam methane reforming process using CaO-Zr/Ni bifunctional sorbent–catalyst

A bifunctional CaO-Zr/Ni (13, 18, and 20.5 wt% NiO) sorbent–catalyst was developed using the wet-mixing/sonication technique and applied for hydrogen production by sorption-enhanced steam methane reforming (SESMR), an intensified process that integrates hydrogen production with CO₂ capture. The material was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and N₂ physisorption (BET). CO₂ sorption efficiency of the developed materials was evaluated during 25 CO₂ sorption/regeneration cycles. The prepared sorbent–catalysts were then applied in the SESMR during 10 reaction cycles. The results showed that the bifunctional sorbent–catalyst with 20.5 wt% NiO loading presented the most suitable activity. The H₂ yield of ∼91% at the end of the 10th SESMR cycle is considerably higher than equilibrium H₂ yield that could be obtained by traditional steam methane reforming.     

Rh/MgO/γ-Al2O3上的毫秒级甲烷蒸汽重整过程

采用负载型Rh/MgO/γ-Al2O3催化剂研究了毫秒级甲烷蒸汽重整过程,在水碳比为1和3的条件下,详细考察了反应温度、空速和催化剂Rh含量对反应转化率和选择性的影响。研究结果表明,Rh/MgO/γ-Al2O3催化剂在毫秒级操作条件下具有良好的催化性能,使用5%(质量分数)Rh催化剂,在水碳比3、反应温度1150K、空速641.11 L·(gcat)-1·h-1时,CH4转化率约90%,CO2选择性约20%,毫秒级接触时间反应行为即可接近热力学平衡。高温有利于毫秒级甲烷蒸汽重整过程。     

Rh/MgO/γ-Al2O3上的毫秒级甲烷蒸汽重整过程

采用负载型Rh/MgO/γ-Al₂O₃催化剂研究了毫秒级甲烷蒸汽重整过程,在水碳比为1和3的条件下,详细考察了反应温度、空速和催化剂Rh含量对反应转化率和选择性的影响。研究结果表明,Rh/MgO/γ-Al₂O₃催化剂在毫秒级操作条件下具有良好的催化性能,使用5%（质量分数）Rh催化剂,在水碳比3、反应温度1150 K、空速641.11 L•（g cat）^-1•h^-1时,CH₄转化率约90%,CO₂选择性约20%,毫秒级接触时间反应行为即可接近热力学平衡。高温有利于毫秒级甲烷蒸汽重整过程。     

Parallel screening of Cu/CeO2/γ-Al2O3 catalysts for steam reforming of methanol in a 10-channel micro-structured reactor

Steam reforming of methanol (SRM) was investigated over Cu/CeO₂/γ-Al₂O₃ catalysts with different compositions in a parallelized 10-channel micro-structured reactor. The catalytic activity was found to be strongly dependent on the copper loading. The parallel screening result was tentatively discussed with surface analysis characterization results and previous proposals. A reaction mechanism is proposed to rationalize the catalytic activity data and characteristics of the catalysts, which supposes that the copper/ceria interfacial area (partially oxidized copper nanoparticle and defective ceria) is the active site for SRM. The oxygen reverse spillover from ceria to copper is suggested to be involved in the catalysis cycle.     

Syngas production via dry reforming of methane over Ni/Al2O3–MgO nanocatalyst synthesized using ultrasound energy

The Ni/Al₂O₃–MgO nanocatalyst with Al/Mg ratio of 1.5 was prepared successfully using sonochemistry method and shown high activity and stability in dry reforming of methane. XRD, BET, FESEM, TEM and EDAX-dot mapping techniques have been used for nanocatalyst characterization. XRD analysis confirmed the formation of MgO and NiO cubic phases. According to the FESEM micrographs, nanostructure grains with uniform surface size distribution have been observed in of the synthesized nanocatalyst. The TEM micrographs showed that ultrasound-assisted preparation method induced uniform morphology without agglomeration of particles. The activity of synthesized nanocatalyst could reach thermodynamic equilibrium conversions and H₂/CO ratios.     

Steam reforming of dimethyl ether over Cu–Ni/γ-Al2O3 bi-functional catalyst：Effect of calcination temperature

采用沉积-沉淀法制备了一系列不同焙烧温度的二甲醚水蒸气重整制氢催化剂2Cu-1Ni/5g-Al₂O₃（摩尔比）,考察了焙烧温度对催化剂2Cu-1Ni/5g-Al₂O₃的结构及催化性能的影响,并运用N₂吸附-脱附（BET）、H₂程序升温还原（H₂-TPR）、X射线衍射（XRD）等手段对催化剂进行了表征与分析。结果表明,500 ℃焙烧的催化剂BET比表面积及孔容、孔径适中。随着焙烧温度的升高,以尖晶石态存在的铜组分比例逐渐增加,金属Cu的粒径也从12.6 nm增至33.2 nm。适当的焙烧温度可保证金属和载体之间的强度适中的作用力,从而保证催化剂具有较优的活性和稳定性。催化剂活性随着焙烧温度的增加先升高后减小,较优的焙烧温度为500 ℃。     

The effect of the addition of Y2O3 to Ni/α-Al2O3 catalysts on the autothermal reforming of methane

The addition of Y₂O₃ to Ni/α-Al₂O₃ catalysts was investigated by BET surface area measurements, hydrogen chemisorption, X-ray diffraction, UV–vis diffuse reflectance spectroscopy, X-ray fluorescence, temperature programmed reduction, temperature programmed oxidation and cyclohexane dehydrogenation. Autothermal reforming experiments were performed in order to evaluate the methane conversion and proceeded through an indirect mechanism consisting of total combustion of methane followed by CO₂ and steam reforming generating the synthesis gas. The Y₂O₃·Al₂O₃ supported catalysts presented better activity and stability in autothermal reforming reaction. Temperature programmed oxidation analysis demonstrated that the addition of Y₂O₃ resulted in a change of the type or the location of coke formed during reaction. None of the prepared catalyst presented deactivation by sintering under the tested conditions. The improved stability of supported catalysts Y₂O₃·Al₂O₃ was the result of minimizing the formation of coke on the surface of nickel particles.     

Steam reforming of liquid petroleum gas over Mn-promoted Ni/γ-Al2O3 catalysts

Three different Mn-promoted Ni/γ-Al₂O₃ catalysts, Mn/Ni/γ-Al₂O₃, Mn-Ni/γ-Al₂O₃ and Ni/Mn/γ-Al₂O₃, were prepared and applied to the steam reforming of liquid petroleum gas (LPG) mainly composed of propane and butane. For comparison, Ni/γ-Al₂O₃ catalysts containing different amount of Ni were also examined. In the case of the Ni/γ-Al₂O₃ catalysts, 4.1 wt% Ni/γ-Al₂O₃ showed the stable catalytic activity with the least amount of coke formation. Among the various Mn-promoted Ni/γ-Al₂O₃ catalysts, Mn/Ni/γ-Al₂O₃ showed the stable catalytic activity with the least amount of coke formation. It also exhibited a similar H₂ formation rate compared with Ni/γ-Al₂O₃. Several characterization techniques—N₂ adsorption/desorption, X-ray diffraction (XRD), CO chemisorptions, temperature-programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS) and CHNS analysis—were employed to characterize the catalysts. The catalytic activity increased with increasing amount of chemisorbed CO for the Mn-promoted Ni/γ-Al₂O₃ catalysts. The highest proportion of Mn⁴⁺ species was observed for the most stable catalyst.     

SO2 Reactions over γ-Al2O3,Pt/γ-Al2O3,Sn/γ-Al2O3 and Pt–Sn/γ-Al2O3

Platinum and Platinum–tin bimetallic catalysts supported on alumina were prepared by co-impregnation of both metallic precursors on the support and used as catalysts for the oxidation of SO₂. Platinum dispersion was determined by means of H₂–O₂ titration. Tin addition (1 and 2 wt%) only slightly decreased the exposed platinum atoms suggesting that tin is mainly over the support. At temperatures lower than 300 °C, SO₂ did not react with oxygen. Nevertheless, when the temperature was increased, the SO₂ oxidation began. The ignition temperatures for SO₂ oxidation (taken at 50% conversion) were 345 °C for 1% Pt/Al₂O₃ and 520 °C for 1% Pt–2% Sn/Al₂O₃. The strong displacement on activity suggests that tin plays an important role as inhibitor of the SO₂ oxidation reaction.     

Transient study of the dry reforming of methane over Pt supported on different γ-Al2O3

CO₂ reforming of methane has been studied over Pt/Al₂O₃ model catalysts in a temperature range of 600–800 °C using steady-state and transient methods (Transient Response Method (TRM) and DRIFT-MS). Pt-supported catalysts were prepared using two different alumina (γ-Al₂O₃(S) Sasol-Puralox and a synthesized γ-Al₂O₃(N) with nanofibrous structure). Catalysts and supports were characterized by conventional methods (XRD, TEM, A_BET, XPS) before and after reaction. Pt⁰ species are present in the catalysts, with a higher relative contribution for the catalyst that has a nanostructured support. Pt/γ-Al₂O₃(N) catalyst presented the best performance in reactivity and showed a low rate of carbon formation and a minimal water production. From TRM and DRIFT-MS results it can be concluded that, when CO₂ and CH₄ are fed separately into the reaction system, they are activated over the catalytic surface. Besides, when both reactants are fed contemporaneously the presence of CH_X species promotes the CO₂ activation that is responsible for the reforming reaction.     

Plasma-driven CO2 hydrogenation to CH3OH over Fe2O3/γ-Al2O3 catalyst

We report a plasma-assisted CO₂ hydrogenation to CH₃OH over Fe₂O₃/γ-Al₂O₃ catalysts, achieving 12% CO₂ conversion and 58% CH₃OH selectivity at a temperature of nearly 80°C atm pressure. We investigated the effect of various supports and loadings of the Fe-based catalysts, as well as optimized reaction conditions. We characterized catalysts by X-ray powder diffraction (XRD), hydrogen temperature programmed reduction (H₂-TPR), CO₂ and CO temperature programmed desorption (CO₂/CO-TPD), high-resolution transmission electron microscopy (HRTEM), scanning transmission electron microscopy (STEM), x-ray photoelectron spectroscopy (XPS), Mössbauer, and Fourier transform infrared ( FTIR). The XPS results show that the enhanced CO₂ conversion and CH₃OH selectivity are attributed to the chemisorbed oxygen species on Fe₂O₃/γ-Al₂O₃. Furthermore, the diffuse reflectance infrared Fourier transform spectroscopy (DRIFTs) and TPD results illustrate that the catalysts with stronger CO₂ adsorption capacity exhibit a higher reaction performance. In situ DRIFTS gain insight into the specific reaction pathways in the CO₂/H₂ plasma. This study reveals the role of chemisorbed oxygen species as a key intermediate, and inspires to design highly efficient catalysts and expand the catalytic systems for CO₂ hydrogenation to CH₃OH.     

Effect of Ce addition on Cr/γ-Al2O3 catalysts for methane catalytic combustion

Cerium modified and chromium-based catalysts using nano-γ-Al₂O₃ as the carrier were prepared via incipient wetness impregnation method and investigated for the catalytic combustion of methane (CH₄). The Cr-based catalysts promoted with 3 wt.% Ce displayed the most effective catalytic activity among all catalysts investigated. In addition, Ce significantly improved the catalytic performance of CH₄ combustion by increasing the amount of reaction site [CrO₄]_ads species on the surface of Cr-based catalysts. Introduction of Ce content also restrained the deactivation of catalysts at high calcination temperature. Cr-based catalysts modified with cerium seem to be a promising cheap and low-temperature catalyst for CH₄ combustion.