Production of Hydrogen from Methane by a CO2 Emission-Suppressed Process: Methane Decomposition and Gasification of Carbon Nanofibers

Catalytic methane decomposition into hydrogen and carbon nanofibers and the oxidations of carbon nanofibers with CO₂, H₂O and O₂ were overviewed. Supported Ni catalysts (Ni/SiO₂, Ni/TiO₂ and Ni/carbon nanofiber) were effective for the methane decomposition. The activity and life of the supported Ni catalysts for methane decomposition strongly depended on the particle size of Ni metal on the catalysts. The modification of the catalysts with Pd enhanced the catalytic activity and life for methane decomposition. In particular, the supported Ni catalysts modified with Pd showed high turnover number of hydrogen formation at temperatures higher than 973 K with a high one-pass methane conversion (>70%). However, sooner or later, every catalyst completely lost their catalytic activities due to the carbon layer formation on active metal surfaces. In order to utilize a large quantity of the carbon nanofibers formed during methane decomposition as a chemical feedstock or a powdered fuel for heat generation, they were oxidized with CO₂, H₂O and O₂ into CO, synthesis gas and CO₂, respectively. In every case, the conversion of carbon was greater than 95%. These oxidations of carbon nanofibers recovered or enhanced the initial activities of the supported Ni catalysts for methane decomposition.     

High-performance supercapacitors of hydrous ruthenium oxide/mesoporous carbon composites

The amorphous hydrous ruthenium oxide/mesoporous carbon composites (denoted as RuO₂·xH₂O/MC), obtained by loading small amount of amorphous hydrous ruthenium oxide nanoparticles ranged from 0.9 to 5.4% by weight of Ru (denoted as RuO₂·xH₂O) on mesoporous carbon (MC), were investigated for the first time and were used for supercapacitors. Electrochemical measurements showed that RuO₂·xH₂O/MC composites not only have an enhanced specific capacitance but also retain the superior rate capability of MC. The RuO₂·xH₂O/MC composite with Ru loading of 3.6 wt% exhibited an increase of the specific capacitance of approximately 57% (from 115 to 181 F/g) at the scan rate of 25 mV s⁻¹ in 0.1 M H₂SO₄ aqueous electrolyte. The specific capacitance based on the mass of RuO₂ was estimated to be 1,527 F/g, by subtracting the contribution from MC in the composite. Cycle performance tests for RuO₂·xH₂O/MC composite (3.6 wt% Ru) showed that approximately 2.8% loss of the total capacitance was observed after 1,000 cycles.     

Pt/MOx(M=Ni,Fe,Co,Ce)催化剂上CO氧化反应中抗H2O与CO2的性能研究

我们研究了4种负载型Pt催化剂（1Pt/NiO、1Pt/FeO_x、1Pt/Co₃O₄和Pt/CeO₂）上不同反应条件下CO氧化活性及抗H₂O和CO₂性能.发现反应气氛中CO₂的加入与CO形成了竞争吸附,并在催化剂表面形成了碳酸盐物种堵塞了活性位,从而导致催化剂失活.反应气氛中H₂O的加入对1Pt/CeO₂催化剂的活性有所抑制,但对1Pt/FeO_x、1Pt/NiO和1Pt/Co₃O₄催化剂的活性却有促进作用.在1Pt/FeO_x和1Pt/CeO₂催化剂上的分步反应实验和动力学研究表明,尽管H₂O的加入在两种催化剂上均与CO形成了竞争吸附,但在1Pt/FeO_x催化剂上H₂O在载体表面解离形成的羟基更易与CO反应,开辟了新的反应途径,从而提高了反应性能.此外,H₂O的加入能有效分解该催化剂上的碳酸盐物种,从而保持了其稳定性.     

FeMn、FeMnNa和FeMnK催化剂上合成气制低碳烯烃的比较

研究了钠、钾助剂对FeMn 合成低碳烯烃催化剂结构及性能的影响. 低温N₂吸附、X射线光电子能谱（XPS）、X射线衍射（XRD）、H₂程序升温还原（H₂-TPR）、CO/CO₂程序升温脱附（CO/CO₂-TPD）、Mössbauer 谱和CO+H₂反应的研究结果表明,增加Mn助剂含量促进了活性相的分散和低碳烯烃的生成,而过多锰助剂在催化剂表面的富集则降低了费托合成反应的CO转化率;钾助剂和钠助剂的加入均抑制了催化剂的还原并且促进了CO₂和CO的吸附. 比较还原后（H₂/CO摩尔比为20）和反应后（H₂/CO摩尔比为3.5）催化剂的体相结构可以发现,在FeMn、FeMnNa和FeMnK催化剂中,由于钾助剂的碱性和CO吸附能力较强,因此体相中FeC_x的含量相对较高;而活性测试结果表明,FeMnNa催化剂拥有最好的CO转化率（96.2%）和低碳烯烃选择性（30.5%,摩尔分数）.     

Cooperative effect of Fe and Ti species over Fe–Ti–Ox catalysts on the catalytic hydrolysis performance of hydrogen cyanide

FeO_x, TiO₂, and Fe–Ti–O_x catalysts were synthesized and used in the catalytic hydrolysis of hydrogen cyanide (HCN). Nearly 100% HCN conversion was achieved at 250 °C over the Fe–Ti–O_x catalyst. TiO₂ rutile was detected over TiO₂, but not over Fe–Ti–O_x, which suggested that the interaction between Fe and Ti species could inhibit the TiO₂ phase transition. Furthermore, the interaction between Fe and Ti species over Fe–Ti–O_x could promote the selectivity of NH₃ and CO. The mechanism of hydrolysis of HCN over FeO_x, TiO₂, and Fe–Ti–O_x can be given as follows: HCN + H₂O → methanamide → ammonium formate → formic acid → H₂O + CO.     

Recent Advances in Preferential Oxidation of CO in H2 Over Gold Catalysts

Recent studies have revealed that supported gold catalysts exhibit comparable or superior catalytic performance relative to platinum group metals, especially at low temperatures, in the preferential oxidation of CO under excess H₂ (CO-PROX). Complete conversion of CO with good selectivity of O₂ for CO₂ and highly stable catalyst performance in the presence of CO₂ and H₂O are considered to be essential for the successful development of CO-PROX catalysts for application in polymer electrolyte membrane fuel cells. The performance of supported gold catalysts in the CO-PROX reaction has been shown to be dependent on the characteristics of gold (size, oxidation state, and its interaction with other metal/oxides), nature of the support (size, composition, preparation method, presence of promoters, and doping with other metal ions), and reaction conditions (temperature and feed composition). Complete CO conversion has been achieved in the presence of certain gold catalysts below 100 °C. The unresolved issues in CO-PROX include the undesired oxidation of H₂, detrimental effects of CO₂ and/or H₂O, and long-term stability of the catalysts. To address these issues, the catalytic activity of gold supported on simple oxides such as TiO₂, CeO₂, Al₂O₃, and Fe₂O₃ has been improved dramatically by the addition of promoters, alteration of the gold-oxide support interface, and modification of the oxide supports. Recently, nanoporous gold has also been recognized to be promising for this reaction. This review highlights recent developments of unsupported and supported gold catalysts for the CO-PROX reaction.     

Widely Controllable Syngas Production by a Dye‐Sensitized TiO2 Hybrid System with ReI and CoIII Catalysts under Visible‐Light Irradiation

Visible‐light irradiation of a ternary hybrid catalyst prepared by grafting a dye, an H₂ evolving Co^III catalyst and a CO‐producing Re^I catalyst on TiO₂ have been found to produce both H₂ and CO (syngas) in CO₂‐saturated N ,N ‐dimethyl formamide (DMF)/water solution containing a 0.1 m sacrificial electron donor. The H₂/CO ratios are effectively controlled by changing either the water content of the solvent or the molar ratio of the Re^I and Co^III catalysts ranging from 1:2 to 15:1. The controlled syngas formation is discussed in terms of competitive electron flow from TiO₂ to each of the CO₂‐reduction and hydrogen‐evolving sites depending on the efficiencies of the two catalytic reaction cycles under given reaction conditions.     

Effect of the microstructure of the supported catalysts CuO/TiO<Subscript>2</Subscript> and CuO/(CeO<Subscript>2</Subscript>-TiO<Subscript>2</Subscript>) on their catalytic properties in carbon monoxide oxidation

The effect of the microstructure of titanium dioxide on the structure, thermal stability, and catalytic properties of supported CuO/TiO₂ and CuO/(CeO₂-TiO₂) catalysts in CO oxidation was studied. The formation of a nanocrystalline structure was found in the CuO/TiO₂ catalysts calcined at 500°C. This nanocrystalline structure consisted of aggregated fine anatase particles about 10 nm in size and interblock boundaries between them, in which Cu²⁺ ions were stabilized. Heat treatment of this catalyst at 700°C led to a change in its microstructure with the formation of fine CuO particles 2.5–3 nm in size, which were strongly bound to the surface of TiO₂ (anatase) with a regular well-ordered crystal structure. In the CuO/(CeO₂-TiO₂) catalysts, the nanocrystalline structure of anatase was thermally more stable than in the CuO/TiO₂ catalyst, and it persisted up to 700°C. The study of the catalytic properties of the resulting catalysts showed that the CuO/(CeO₂-TiO₂) catalysts with the nanocrystalline structure of anatase were characterized by the high-est activity in CO oxidation to CO₂.     

Facile synthesis of WOx/ZrO2 catalysts using WO3·H2O precipitate as synthetic precursor of active tungsten species

Zirconia-supported tungsten oxide (WO_x/ZrO₂) catalysts were successfully synthesized using a suspension containing amorphous hydrous zirconia precipitates [ZrO_x(OH)_4-2x·yH₂O]_n and tungstate monohydrate (WO₃·H₂O) precipitates. The procedure involved the dissolution of the WO₃·H₂O precipitate during the aging process with the release of oxyanion [WO₄]^2- species, interaction of this species with the surface of the [ZrO_x(OH)_4-2x·yH₂O]_n precipitate and, formation of active WO_x species after thermal treatment. Non-bridging hydroxyl (OH^?) groups present in the [ZrO_x(OH)_4-2x·yH₂O]_n precipitate act as an active agent for the WO₃·H₂O dissolution. N₂ physisorption, X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), temperature-programmed reduction using hydrogen (H₂-TPR), temperature-programmed desorption of ammonia (NH₃-TPD), Fourier-transform infrared (FTIR) spectroscopy of adsorbed pyridine, and Raman spectroscopy were used to elucidate the catalyst structure–performance relationship. The catalytic activity was evaluated for the oxidative desulfurization (ODS) of a model fuel containing dibenzothiophene (DBT). For a fixed WO₃·H₂O content, longer aging times improved the catalyst activity, reaching a maximum when WO₃·H₂O was completely dissolved. The increase in surface area and formation of more active Zr-WO_x clusters and polytungstates are observed for the highest active catalysts. A synergetic effect between local Lewis and Brønsted acid sites seems to have contributed to the observed superior activity. The proposed strategy provides an efficient approach to produce active WO_x/ZrO₂ catalysts and may be applicable for designing other heterogeneous catalytic systems.     

Avoiding Self‐Poisoning: A Key Feature for the High Activity of Au/Mg(OH)2 Catalysts in Continuous Low‐Temperature CO Oxidation

Au/Mg(OH)₂ catalysts have been reported to be far more active in the catalytic low‐temperature CO oxidation (below 0 °C) than the thoroughly investigated Au/TiO₂ catalysts. Based on kinetic and in situ infrared spectroscopy (DRIFTS) measurements, we demonstrate that the comparatively weak interaction of Au/Mg(OH)₂ with CO₂ formed during the low‐temperature reaction is the main reason for the superior catalyst performance. This feature enables rapid product desorption and hence continuous CO oxidation at temperatures well below 0 °C. At these temperatures, Au/TiO₂ also catalyzes CO₂ formation, but does not allow for CO₂ desorption, which results in self‐poisoning. At higher temperatures (above 0 °C), however, CO₂ formation is rate‐limiting, which results in a much higher activity for Au/TiO₂ under these reaction conditions.     

助剂对NiMgAl催化剂的结构和甲烷二氧化碳重整反应性能的影响(英文)

向担载镍基催化剂NiMgAl中添加助剂(Co,Ir或Pt)制备了三种助剂促进型催化剂,通过氢气程序升温还原(H2-TPR),CO2/CH4程序升温表面反应(CO2/CH4-TPSR)和CO2程序升温脱附(CO2-TPD)等方法对催化剂进行表征.助剂对催化剂性能的影响通过甲烷干重整实验进行评价.添加少量的Pt或Ir助剂可以降低Ni活性组分的还原温度和提高反应性能.添加助剂的样品与原始NiMgAl催化剂相比能够降低反应的活化能,添加Co或Ir助剂的催化剂与NiMgAl催化剂相比活化能有了明显的降低.NiMgAl催化剂的活化能为51.8 kJ·mol-1,添加Pt助剂的NiPtMgAl催化剂活化能降至26.4 kJ·mol-1.NiMgAl催化剂中添加Pt助剂制备的催化剂具有较好的催化活性和较低的活化能.CH4-TPSR和CO2-TPSR结果表明添加Pt助剂可以在更低的温度下(与NiMgAl催化剂相比)提高CH4的活化能力,并在催化剂表面形成更多的碳物种.CO2-TPD结果显示,添加助剂的催化剂与NiMgAl样品相比在反应温度区间内增加了CO2的吸附/脱附量.     

Promotion effect of adsorbed water/OH on the catalytic performance of Ag/activated carbon catalysts for CO preferential oxidation in excess H2

Activated carbon (AC) supported silver catalysts were prepared by incipient wetness impregnation method and their catalytic performance for CO preferential oxidation (PROX) in excess H₂ was evaluated. Ag/AC catalysts, after reduction in H₂ at low temperatures (≤200 °C) following heat treatment in He at 200 °C (He200H200), exhibited the best catalytic properties. Temperature-programmed desorption (TPD), X-ray diffraction (XRD) and temperature-programmed reduction (TPR) results indicated that silver oxides were produced during heat treatment in He at 200 °C which were reduced to metal silver nanoparticles in H₂ at low temperatures (≤200 °C), simultaneously generating the adsorbed water/OH. CO conversion was enhanced 40% after water treatment following heat treatment in He at 600 °C. These results imply that the metal silver nanoparticles are the active species and the adsorbed water/OH has noticeable promotion effects on CO oxidation. However, the promotion effect is still limited compared to gold catalysts under the similar conditions, which may be the reason of low selectivity to CO oxidation in PROX over silver catalysts. The reported Ag/AC-S-He catalyst after He200H₂00 treatment displayed similar PROX of CO reaction properties to Ag/SiO₂. This means that Ag/AC catalyst is also an efficient low-temperature CO oxidation catalyst.     

Selective hydrogenation of citral over Au-based bimetallic catalysts in supercritical carbon dioxide

Selective hydrogenation of citral was investigated over Au-based bimetallic catalysts in the environmentally benign supercritical carbon dioxide (scCO₂) medium. The catalytic performances were different in citral hydrogenation when Pd or Ru was mixed (physically and chemically) with Au. Compared with the corresponding monometallic catalyst, the total conversion and the selectivity to citronellal (CAL) were significantly enhanced over TiO₂ supported Pd and Au bimetallic catalysts (physically and chemically mixed); however, the conversion and selectivity did not change when Ru was physically mixed with Au catalyst compared to the monometallic Ru/TiO₂, and the chemically mixed Ru-Au/TiO₂ catalyst did not show any activity. The effect of CO₂ pressure on the conversion of citral and product selectivity was significantly different over the Au/TiO₂, Pd-Au/TiO₂, and Pd/TiO₂ catalysts. It was assumed to be ascribed to the difference in the interactions between Au, Pd nanoparticles and CO₂ under different CO₂ pressures.     

Microwave-assisted synthesis of organic–inorganic poly(3,4-ethylenedioxythiophene)/RuO2·xH2O nanocomposite for supercapacitor

An organic–inorganic poly(3,4-ethylenedioxythiophene) (PEDOT)/RuO₂·xH₂O nanocomposite (approximately 1 wt.% RuO₂) has been successfully prepared for the first time under microwave irradiation within 5 min with power 900 W via in situ chemical polymerization. The morphology and structure of the resultant material is characterized by transmission electron microscope and Fourier transform infrared. Moreover, the electrochemical properties of the synthesized nanocomposite can be controlled by adjusting the annealing temperature, which is definitely illustrated by cyclic voltammetry, galvanostatic charge–discharge, and electrochemical impedance spectra. Electrochemical data have shown that the PEDOT/RuO₂·xH₂O nanocomposite annealed at 150 °C possesses the most favorable charge/discharge ability with a specific capacitance of 153.3 F g⁻¹ at a current density of 150 mA g⁻¹ and the high efficient utilization of PEDOT at various current densities. Furthermore, such composite has a less capacitance degradation of 23.8% after 1,000 continuous cycles. The improved electrochemical performance are mainly attributed to the large electroactive surface of nanocomposite and the existence of amorphous RuO₂·xH₂O particles as well as a synergistic effect of the polymer PEDOT and annealed RuO₂·xH₂O. Thus, the PEDOT/RuO₂·xH₂O nanocomposite annealed at 150 °C can act as a promising electroactive material for supercapacitor application.     

Multiwalled Carbon Nanotubes Encased in Ruthenium Oxide Film as a Hybrid Material for Neurotransmitters Sensor

A hybrid film (MWCNTs‐RuO_x?nH₂O) which contains multiwalled carbon nanotubes (MWCNTs) along with the incorporation of ruthenium oxide (RuO_x?nH₂O) has been synthesized on glassy carbon electrode (GCE), gold (Au), indium tin oxide (ITO) and screen printed carbon electrode (SPCE) by potentiostatic methods. The presence of MWCNTs in the hybrid film enhances surface coverage concentration (Γ) of RuO_x?nH₂O to ≈2100%. The surface morphology of the hybrid film deposited on ITO has been studied using scanning electron microscopy and atomic force microscopy. These two techniques reveal that the RuO_x?nH₂O incorporated on MWCNTs. Electrochemical quartz crystal microbalance study too reveals the incorporation of MWCNTs and RuO_x?nH₂O. The MWCNTs‐RuO_x?nH₂O hybrid film exhibits promising enhanced electrocatalytic activity towards the biochemical compounds such as epinephrine and norepinephrine. The electrocatalytic responses of these analytes at RuO_x?nH₂O, MWCNTs and MWCNTs‐RuO_x?nH₂O hybrid films have been measured using cyclic voltammetry. The obtained sensitivity values from electrocatalysis studies of analytes for MWCNTs‐RuO_x?nH₂O hybrid film are higher than the RuO_x?nH₂O and MWCNTs films. Finally, the flow injection analysis has been used for the amperometric studies of analytes at MWCNTs‐RuO_x?nH₂O hybrid film modified SPCEs.     

Effective tri-metallic TiO2 supported catalyst for hydrocarbon production from carbon dioxide

The current socio-economic issues with concerns on environmental quality and global warming are attributed to high concentrations of atmospheric carbon dioxide due to extensive usage of fossil fuels. Thus, over the last two decades, comprehensive work has been reported on carbon capture and storage and catalytic conversion of carbon dioxide to hydrocarbons. Among these, the reactions with hydrocarbons to form value-added products have been in focus. In this work, an attempt was made to identify the feasibility of the reaction: carbon dioxide and steam to form hydrocarbons of fuel value. After reviewing the literature on the development of various catalysts and their mechanism, a multi-metallic catalyst supported by TiO₂ Nano-needles was explored. The reaction mechanism is expected to proceed with activated CO₂ complex and hydroxyl groups over the metal oxide catalyst. Current reported work on CO₂ and Hydrogen proceeds with activated CO₂ and protons over the catalyst. The characterization techniques mainly XPS, XRD, TGA, FESEM-EDAX, FTIR, and NMR were used to analyze the catalyst activity and to confirm the products formed. The reaction is found to yield methanol and oxygen only. However, the conversion is found to be 0.4% - 3.8% in the temperature range 350°C to 550°C. The reaction of CO₂ with hydroxyl groups from water vapor can be effective as an alternative to the reaction with protons from hydrogen.     

Copolymerization of carbon dioxide with cyclohexene oxide catalyzed by bimetallic dysprosium complexes containing hydrazine‐functionalized Schiff‐base derivatives

A series of dinuclear Dy^III acetate complexes containing three different hydrazine‐functionalized Schiff‐base ligands ( hmb , hmi, and hb ) have been synthesized by one‐pot reaction with Dy(OAc)₃·4H₂O as the metal precursor. [Dy₂( hmb )₂(OAc)₄]·MeCN ( 1 ·MeCN) and [Dy₂( hmi )₂(OAc)₂(MeOH)₂]·H₂O ( 2 ·H₂O) with keto and enol forms of the corresponding ligands, respectively, were shown the similar core structures but different ratio of Dy^III to OAc^–. Moreover, the different coordination environments of complex [Dy₂( hb )₂(μ‐OAc)₂(OAc)₂(H₂O)₂]·DMF·H₂O ( 3 ·DMF·H₂O) also offered an opportunity to understand the relationship between structural model and catalytic properties. Bimetallic dysprosium complexes 1 – 3 were demonstrated to be active catalysts for copolymerization of carbon dioxide (CO₂) and cyclohexene oxide (CHO) without cocatalysts. To the best of our knowledge, well‐defined catalyst 2 appears to be the first example of an air‐stable bimetallic dysprosium complex that is effective for CO₂/CHO copolymerization and the formation of the perfectly alternating poly(cyclohexenecarbonate) with a high molecular weight. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 321–328     

Study of K/Mn-MgO Supported Fe Catalysts with Fe（CO）5 and Fe（NO3）3 as Precursors for CO Hydrogenation to Light Alkenes

Two K/Mn-MgO supported catalysts were prepared by Fe（CO）5 and Fe（NO3）3 as precursor respectively. The obtained Fe-K/Mn-MgO catalysts were tested for CO hydrogenation to light alkenes and characterized by X-ray powder diffraction （XRD）, X-ray photoelectron spectra （XPS）, H2 temperature-programmed reduction （H2-TPR）, H2 CO and CO2 temperature-programmed desorption （H2, CO/CO2-TPD） and transmission electron microscope （TEM） The results indicated that the catalyst with 10 wt% Fe loading prepared by Fe（CO）5 as precursor showed better performance in syngas to light alkenes than ones obtained from Fe（NO3）3 as precursor, where the CO conversion was 62.50% and the selectivity was 55.95% at 350 ℃, 1.5 MPa and 1000 h^-1, respectively.     

Effect of Nano‐support and Type of Active Metal on Reforming of CH4 with CO2

Two series of Co and Ni based catalysts supported over commercial (ZrO₂, CeO₂, and Al₂O₃) nano supports were investigated for dry reforming of methane. The catalytic activity of both Co and Ni based catalysts were assessed at different reaction temperatures ranging from 500—800 °C; however, for stability the time on stream experiments were conducted at 700 °C for 6 h. Various techniques such as N₂ adsorption‐desorption isotherm, temperature‐programmed reduction (H₂‐TPR), temperature‐programmed desorption (CO₂‐TPD), temperature‐programmed oxidation (TPO), X‐ray diffraction (XRD), thermogravimetric analysis (TGA) were applied for characterization of fresh and spent catalysts. The catalytic activity and stability tests clearly showed that the performance of catalyst is strongly dependent on type of active metal and support. Furthermore, active metal particle size and Lewis basicity are key factors which have significant influence on catalytic performance. The results indicated that Ni supported over nano ZrO₂ exhibited highest activity among all tested catalysts due to its unique properties including thermal stability and reducibility. The minimum carbon deposition and thus relatively stable performance was observed in case of Co‐Al catalyst, since this catalyst has shown highest Lewis basicity.     

Highly Efficient Hydrogenation of Methyl Propionate to Propanol over Hydrous Zirconia Supported Ruthenium

Hydrous zirconia supported ruthenium catalyst Ru/ZrO₂·xH₂O, prepared by co‐precipitating ruthenium trichloride and zirconium oxychloride with ammonia, was able to catalyze efficiently methyl propionate to propanol under the mild conditions. In aqueous system, the propanol yield of >99% was achieved under the conditions of reaction temperature of 150°C and hydrogen pressure of 5.0 MPa, while in non‐aqueous system the maximum propanol yield was only 47.0%. FTIR spectra and hydrogenation results indicated that the high catalytic performance of Ru/ZrO₂·xH₂O in aqueous phase results from the cooperation effect between water as a solvent and hydroxyl groups on the surface of carrier.