Hydrogen production by aqueous-phase reforming of ethanol over nickel catalysts prepared from hydrotalcite precursors

Derived hydrotalcite catalysts, with different Ni loadings, were prepared and tested in aqueous-phase reforming of ethanol. Upon calcination of the hydrotalcite-like compounds, there was formation of MgO periclase-type phase, where both nickel and aluminum oxides are well dispersed. The mixed oxides showed only one reduction peak in temperature range of 900–1000 °C. The catalytic tests were carried out in a batch reactor with an aqueous solution of 1 wt.% ethanol at different temperatures (200, 230 and 250 °C). The derived hydrotalcite catalysts showed high activity, with 65% of ethanol conversion at 230 °C, high hydrogen selectivity and lower methane production than alumina supported nickel catalyst.     

Investigation of the catalytic performance of Ni/MgO catalysts in partial oxidation,dry reforming and combined reforming of methane

Dry reforming, partial oxidation and combined reforming of methane (combination of partial oxidation and dry reforming) to synthesis gas over nickel catalysts supported on nanocrystalline magnesium oxide with various nickel loadings have been studied. Among the catalysts evaluated, catalyst with 15 wt.% nickel content revealed the most active catalytic performance toward dry reforming, partial oxidation and combined reforming reactions. In addition, catalyst with 5 wt.% nickel loading was employed in long term stability test and has shown stable catalytic performance up to 50 h time on stream without any decrease in methane conversion in these three processes.     

Preparation of noble metal nanocatalysts and their applications in catalytic partial oxidation of methane

A series of noble metal catalysts (Ru, Rh, Ir, Pt, and Pd) supported on alumina-stabilized magnesia were prepared and employed in partial oxidation of methane. The prepared catalysts were characterized using BET, SEM, TEM and H₂S chemisorption techniques. The results revealed that the Ru and Rh catalysts had the highest activity in catalytic partial oxidation of methane. Based on the obtained results the following order of activity was observed for different catalysts in partial oxidation of methane: Rh ～ Ru > Ir > Pt > Pd. The obtained results also showed a high catalytic stability without any decrease in methane conversion up to 50 h of reaction.     

Combination of flame synthesis and high-throughput experimentation: The preparation of alumina-supported noble metal particles and their application in the partial oxidation of methane

Mono and multi-noble metal particles on Al₂O₃ were prepared in one step by flame spray pyrolysis (FSP) of the corresponding noble metal precursors dissolved in methanol and acetic acid (v/v 1:1) or xylene. The noble metal loading of the catalysts was close to the theoretical composition as determined by WD-XRF and LA-ICP-MS. The preparation method was combined with high-throughput testing using an experimental setup consisting of eight parallel fixed-bed reactors. Samples containing 0.1–5 wt% noble metals (Ru, Rh, Pt, Pd) on Al₂O₃ were tested in the catalytic partial oxidation of methane. The ignition of the reaction towards carbon monoxide and hydrogen depended on the loading and the noble metal constituents. The selectivity of these noble metal catalysts towards CO and H₂ was similar under the conditions used (methane: oxygen ratio 2:1, temperature from 300 to 500 °C) and exceeded significantly those of gold and silver containing catalysts.Selected catalysts were further analysed using XPS, BET, STEM-EDXS and XANES/EXAFS. The catalysts exhibited generally a specific surface area of more than 100 m²/g, and were made up of ca. 10 nm alumina particles on which the smaller noble metal particles (1–2 nm, partially oxidized state) were discernible. XPS investigation revealed an enrichment of noble metals on the alumina surface of all samples. The question of alloy formation was addressed by STEM-EDXS and EXAFS analysis. In some cases, particularly for Pt–Pd and Pt–Rh, alloying close to the bulk alloys was found, in contrast to Pt–Ru being only partially alloyed. In situ X-ray absorption spectroscopy on selected samples was used to gain insight into the oxidation state during ignition and extinction of the catalytic partial oxidation of methane to hydrogen and carbon monoxide.     

Catalytic activity evaluation for hydrogen production via autothermal reforming of methane

A nickel catalyst (5.75 wt.%) supported on gamma-alumina was evaluated through autothermal reforming of methane (ATR). The reforming process was pointed to hydrogen production, following thermodynamic and stoichiometric predictions. The catalyst was characterised by several methods including atomic absorption spectroscopy (AAS), B.E.T.-N₂, X-ray diffraction (XRD), scanning electron microscope (SEM) and thermal analyses (thermogravimetry, TG; derivate thermogravimetry, DTG; and differential thermal analysis, DTA). Experimental evaluations in a fixed-bed reactor (1023–1123 K, 1.00 bar, 150–400 cm³/min feed) presented methane conversions in the range of 40–65%. The effluent mixtures provided hydrogen yields in the range of 78–84%, carbon monoxide 3–14%, and carbon dioxide 5–18%. High molar H₂/CO ratios, ranging from 8 to 90, were obtained. Operating autothermal conditions (excess of steam, 1023–1123 K, 1.00 bar) provided low coke formation and high hydrogen selectivity (81%) for methane reforming.     

Oxidative coupling of methane over calcium chloride-promoted calcium chlorophosphate

CaCl₂-promoted calcium chlorophosphate catalysts exhibited high catalytic performance for oxidative coupling of methane (OCM), while unpromoted calcium chlorapatite and calcium chlorophosphate exhibited poor catalytic performance. The presence of CaCl₂ also yielded high ethene selectivity. Partial substitution of the calcium with transition metals, such as zinc, lead and nickel further enhanced the catalytic performance at 973 K; the optimum extent of substitution was about 4%. At 1023 K, however, the effect of substitution appeared to be little. Too excessive substitution gave rise to a decrease of the activity. At 1023 K, the highest C₂ yield of around 22% was obtained with the C₂ selectivity of 56–59%. The C₂H₄ selectivity was also high, around 50%. Production of a significant amount of H₂ was observed over the CaCl₂-promoted calcium chlorophosphate catalysts. We propose that the major pathways for the production of H₂ are the steam reforming and partial oxidation of ethane and ethene which accompany simultaneous production of CO.     

Hydrogenation of carbon monoxide to methane over mesoporous nickel-M-alumina (M = Fe,Ni, Co,Ce, and La) xerogel catalysts

Mesoporous nickel(30 wt%)-M(10 wt%)-alumina xerogel (30Ni10MAX) catalysts with different second metal (M = Fe, Ni, Co, Ce, and La) were prepared by a single-step sol–gel method for use in the methane production from carbon monoxide and hydrogen. In the methanation reaction, yield for CH₄ decreased in the order of 30Ni10FeAX > 30Ni10NiAX > 30Ni10CoAX > 30Ni10CeAX > 30Ni10LaAX. Experimental results revealed that CO dissociation energy of the catalyst and H₂ adsorption ability of the catalyst played a key role in determining the catalytic performance of 30Ni10MAX catalyst in the methanation reaction. Optimal CO dissociation energy of the catalyst and large H₂ adsorption ability of the catalyst were favorable for methane production. Among the catalysts tested, 30Ni10FeAX catalyst with the most optimal CO dissociation energy and the largest H₂ adsorption ability exhibited the best catalytic performance in terms of conversion of CO and yield for CH₄ in the methanation reaction. The enhanced catalytic performance of 30Ni10FeAX was also due to a formation of nickel–iron alloy and a facile reduction.     

One-pot synthesis of nickel sulfide with sulfur powder as sulfur source in solution and their electrochemical properties for hydrogen evolution reaction

Among low-cost and earth-abundant elements, the nickel-based HER catalysts, particularly nickel sulfide, are considered as one of the most promising candidates in this field. In this paper, a kind of spherical nickel sulfide material was obtained using nickel acetate and sulfur powder as precursors by one-pot synthesis. The use of sulfur powder as sulfur source with solution-based method will enable the synthesis of metal sulfides to be more simple and capable of mass production. In addition, the as-synthesized nickel sulfide exhibits an onset overpotential of as low as 25 mV, a Tafel slope of 90 mV dec^− 1, and an exchange current density of 0.44 mA cm^− 2. Furthermore, this catalyst maintains its catalytic activity for at least 25 h and only requires overpotentials of 42 and 113 mV to attain current densities of 2 and 10 mA cm^− 2, respectively. The electrocatalytic performance is promising for applications as non-noble-metal HER catalyst with water splitting for hydrogen production.     

Potassium-modified molybdenum-containing SBA-15 catalysts for highly efficient production of acetaldehyde and ethylene by the selective oxidation of ethane

Mo-incorporated SBA-15 (Mo-SBA-15) catalysts with different Mo:Si molar ratios were synthesized by a direct hydrothermal method, and SBA-15-supported Mo catalysts (Mo/SBA-15 and K-Mo/SBA-15) were prepared by an incipient-wetness impregnation method. The structures of the catalysts were characterized by means of N₂ adsorption–desorption, XRD, TEM, FT-IR, and UV-Raman, and their catalytic performance for the oxidation of ethane was tested. Turnover frequency and product selectivity are strongly dependent on the molybdenum content and catalyst preparation method. Furthermore, the addition of potassium promotes the formation of isolated tetra-coordination molybdenum species and potassium molybdate. The K/Mo-SBA-15 catalysts possess much higher catalytic selectivity to acetaldehyde in the selective oxidation of ethane than the supported molybdenum catalysts (Mo/SBA-15 or K-Mo/SBA-15). The highest selectivity of CH₃CHO + C₂H₄ 68.3% is obtained over the K/Mo-SBA-15 catalyst. Analysis of kinetic results supports the conclusion that ethane oxidation is the first-order reaction and ethane activation may be the rate-determining step for the oxidation of ethane. Ethylene is a possible intermediate for acetaldehyde formation.     

Hydrogen production by partial oxidation of methanol over bimetallic Au–Ru/Fe2O3 catalysts

Hydrogen production by partial oxidation of methanol (POM) was investigated over Au–Ru/Fe₂O₃ catalyst, prepared by deposition–precipitation. The activity of Au–Ru/Fe₂O₃ catalyst was compared with bulk Fe₂O₃, Au/Fe₂O₃ and Ru/Fe₂O₃ catalysts. The reaction parameters, such as O₂/CH₃OH molar ratio, calcination temperature and reaction temperature were optimized. The catalysts were characterized by ICP, XRD, TEM and TPR analyses. The catalytic activity towards hydrogen formation is found to be higher over the bimetallic Au–Ru/Fe₂O₃ catalyst compared to the monometallic Au/Fe₂O₃ and Ru/Fe₂O₃ catalysts. Bulk Fe₂O₃ showed negligible activity towards hydrogen formation. The enhanced activity and stability of the bimetallic Au–Ru/Fe₂O₃ catalyst has been explained in terms of strong metal–metal and metal–support interactions. The catalytic activity was found to depend on the partial pressure of oxygen, which also plays an important role in determining the product distribution. The catalytic behavior at various calcination temperatures suggests that chemical state of the support and particle size of Au and Ru plays an important role. The optimum calcination temperature for hydrogen selectivity is 673 K. The catalytic performance at various reaction temperatures, between 433 and 553 K shows that complete consumption of oxygen is observed at 493 K. Methanol conversion increases with rise in temperature and attains 100% at 523 K; hydrogen selectivity also increases with rise in temperature and reaches 92% at 553 K. The overall reactions involved are suggested as consecutive methanol combustion, partial oxidation, steam reforming and decomposition. CO produced by methanol decomposition is subsequently transformed into CO₂ by the water gas shift and CO oxidation reactions.     

Vapor-phase selective hydrogenation of maleic anhydride to succinic anhydride over Ni/TiO2 catalysts

A series of supported Ni/TiO₂ catalysts were prepared by incipient wetness impregnation method under different calcination temperatures, and the as-prepared catalysts were characterized by X-ray diffraction (XRD), hydrogen temperature-programmed reduction (H₂-TPR) and X-ray photoelectron spectroscopy (XPS). The catalytic properties of these Ni/TiO₂ catalysts were investigated in the vapor phase hydrogenation of maleic anhydride (MA) to succinic anhydride (SA). The results showed that the catalytic activity and the selectivity of the Ni/TiO₂ catalysts were strongly affected by the calcination temperature. The catalyst calcined at 1023 K showed a relatively higher SA selectivity of 96% at high MA conversion (96%) under the tested conditions (493 K and 0.2 MPa). The improvement of SA selectivity could be mainly assigned to the presence of suitable metal–support interaction, which can play a role in catalytic property of active nickel species as electron promoter. Besides, the change of surface properties of TiO₂ support with the increasing calcination temperatures, e.g., the decrease of Lewis acid sites, might also have some positive role in reducing the side-products like γ-butyrolacetone (GBL).     

Au/Ti-SBA-15 catalysts in CO and preferential (PROX) CO oxidation

The Au/Ti-SBA-15 catalysts were found promising for CO oxidation, including preferential CO oxidation in the presence of H₂ (PROX). The catalytic performance and Au particle size depending on the Ti content: 100% selectivity to CO₂ in PROX at 90% CO conversion was found for the catalysts of the Ti content below 1.32 wt.% Ti.     

Tunable ceria–zirconia support for nickel–cobalt catalyst in the enhancement of methane dry reforming with carbon dioxide

Ceria–zirconia mixed oxides (CeZr) were glycol-thermally synthesised as nano-crystalline supports with tunable ratios for the anchoring of nickel–cobalt (Ni–Co) catalyst to enhance methane dry reforming (MDR) reaction with carbon dioxide. High conversion of methane (90%) and carbon dioxide (92%), good output (H₂ = 32%; CO = 44%), and selectivity and stability of syngas prove the effectiveness of the catalyst deposited on this support. 80:20 for Ce:Zr was identified as the optimal ratio to attain active and stable catalytic performance in MDR, with a low coking content of 0.47 wt.%.     

Zirconia: Selective oxidation catalyst for removal of tar and ammonia from biomass gasification gas

Catalysts containing zirconia and alumina were tested for their activity in the selective oxidation of tar and ammonia in biomass gasification gas. Their performance was compared with that of nickel and dolomite catalysts. Synthetic gasification gas with toluene as tar model compound was used as feed. In the presence of oxygen, zirconia and alumina-doped zirconia gave high toluene and ammonia conversions even below 600 °C. They were the most active catalysts for toluene oxidation below 700 °C and for ammonia oxidation below 650 °C. At higher temperatures than these, the impregnated ZrO₂/Al₂O₃ catalysts performed better: oxidation selectivity was improved and toluene and ammonia conversions were higher. The presence of both zirconia and alumina in the catalyst promoted toluene and ammonia conversions at low temperatures: zirconia enhanced the oxidation activity, while alumina improved the oxidation selectivity. The presence of H₂S had little effect on the activity of alumina-doped zirconia.     

Fischer–Tropsch synthesis: effect of small amounts of boron,ruthenium and rhenium on Co/TiO2 catalysts

The effect of the addition of small amounts of boron, ruthenium and rhenium on the Fischer–Tropsch (F–T) catalyst activity and selectivity of a 10 wt.% Co/TiO₂ catalyst has been investigated in a continuously stirred tank reactor (CSTR). A wide range of synthesis gas conversions has been obtained by varying space velocities over the catalysts. The addition of a small amount of boron (0.05 wt.%) onto Co/TiO₂ does not change the activity of the catalyst at lower space times and slightly increases synthesis gas conversion at higher space times. The product selectivity is not significantly influenced by boron addition for all space velocities investigated. Ruthenium addition (0.20 wt.%) onto Co/TiO₂ and CoB/TiO₂ catalysts improves the catalyst activity and selectivity. At a space time of 0.5 h-g cat./NL, synthesis gas conversion increases from 50–54 to 68–71% range and methane selectivity decreases from 9.5 to 5.5% (molar carbon basis) for the promoted catalyst. Among the five promoted and non-promoted catalysts, the rhenium promoted Co/TiO₂ catalyst (0.34 wt.% Re) exhibited the highest synthesis gas conversion, and at a space time of 0.5 h-g cat./NL, synthesis gas conversion was 73.4%. In comparison with the results obtained in a fixed bed reactor, the catalysts displayed a higher F–T catalytic activity in the CSTR.     

Hydrogen production from glycerol steam reforming over molybdena–alumina catalysts

The glycerol steam reforming was investigated on alumina supported molybdena catalysts (with 2, 5 and 12 wt.%) prepared by the sol–gel method and gel combustion. The catalysts were characterized by XRD, BET, UV–VIS, DRIFT, SEM and TEM. The catalytic performances were studied at 400–500 °C, steam to glycerol molar ratio between 9:1 and 20:1 and feed flow rate 0.04–0.08 ml/min. The conversion is directly proportional to molybdena loading, while the hydrogen selectivity has reached greater value on catalyst with 2% MoO₃. The optimum ratio steam to glycerol for reforming is 15:1 and for decomposition in syngas 9:1 and the ratio 20:1 favors water gas shift reaction.     

Catalytic oxidation of methane over KCl-LnCl3 eutectic molten salts

The study of the partial oxidation of methane (POM) over KCl-LnCl₃ (Ln = La, Ce, Sm, Dy, Yb) eutectic molten salts was undertaken. The reaction main products were hydrocarbons (primarily C2, selectivity > 70%). The formation of hydrogen was never detected. The catalytic performance is clearly dependent on the rare earth ions properties and the factors that seem to contribute to the variation of the activity and selectivity along the lanthanide series are the mobility and the oxidative character of the rare earth trivalent ions in the potassium chloride molten melt. The activity increases with the molten salts eutetic melting temperatures and the selectivity to hydrocarbons decreases with the oxidative character of rare earth ions. To our knowledge, this is the first time that POM was studied over chloride base rare earth molten salts.     

Temperature profile in a two-stage fixed bed reactor for catalytic partial oxidation of methane to syngas

Detailed axial temperature distribution has been studied in a two-stage process for catalytic partial oxidation of methane to syngas, which consists of two consecutive fixed bed reactors with oxygen or air separately introduced. The first stage of the reactor, packed with a combustion catalyst, is used for catalytic combustion of methane at low initial temperature. While the second stage, filled with a partial oxidation catalyst, is used for the partial oxidation of methane to syngas. A pilot-scale reactor packed with up to 80 g combustion catalyst and 80 g partial oxidation catalyst was employed. The effects of oxygen distribution in the two sections, and gas hourly space velocity (GHSV) on the catalyst bed temperature profile, as well as conversion of methane and selectivities to syngas were investigated under atmospheric pressure. It is found that both oxygen splitting ratio and GHSV have significant influence on the temperature profile in the reactor, which can be explained by the synergetic effects of the fast exothermic oxidation reactions and the slow endothermic (steam and CO₂) reforming reactions. Almost no change in activity and selectivity was observed after a stability experiment for 300 h.     

Surface modification of Ni catalysts with trace Pt for oxidative steam reforming of methane

Hysteresis of catalytic performance with respect to temperature increasing and decreasing in oxidative steam reforming of methane (CH₄/H₂O/O₂/Ar = 40/30/20/10) over the monometallic Ni catalysts disappeared by the modification with Pt, and the additive effect of Pt by the sequential impregnation method (Pt/Ni) was much more significant than that by the co-impregnation method (Pt + Ni) in terms of catalytic performance and catalyst bed temperature profile. Characterization results by means of TEM, TPR, EXAFS, and FTIR suggest that the Pt atoms on the Pt/Ni catalysts were located more preferably on the surface to form a PtNi alloy than those on the Pt + Ni catalysts. The modification of Ni with Pt suppressed the oxidation of Ni species near the bed inlet in the oxidative steam reforming of methane at 1123 K, although the species on the monometallic Ni catalysts were oxidized under similar conditions. This can be due to the decreased oxidation rate of the species and the increased reduction rate caused by the surface modification of Ni with Pt. Consequently, the PtNi species can be maintained in the metallic state near the bed inlet, and the species can be the active site for the reforming reaction as well as the combustion reaction, which this leads to a lower bed temperature and smaller temperature gradient than those seen for the monometallic Ni catalysts.     

Non-oxidative conversion of ethane to ethylene over transition metals supported on Mg–Al mixed oxide: Preliminary screening of catalytic activity and coking ability

Conversion of ethane into ethylene and hydrogen at 700 °C over pre-reduced Mg–Al mixed oxide-supported transition metal M catalysts (M = Cr, Fe, Co, Ni, Cu) has been studied. The catalysts were prepared from layered double hydroxide precursors synthesized by conventional coprecipitation of metal cations under basic conditions. The results of preliminary screening tests revealed that among all catalysts the chromium-containing material demonstrated the most attractive catalytic behavior showing ethane conversion markedly higher than with other catalysts, considerably high selectivity to ethylene, and a low coking ability.