Hydrogen production from catalytic decomposition of methane over ordered mesoporous carbons (CMK-3) and carbide-derived carbon (DUT-19)

This paper presents a thermogravimetric analysis of catalytic methane decomposition using ordered mesoporous carbon nanorods (CMK-3) and ordered mesoporous carbide-derived carbon (DUT-19) as catalysts. X-ray diffraction and N₂ physisorption analyses were performed for both fresh catalysts. Threshold temperatures for methane decomposition with DUT-19 and CMK-3 were estimated by three different methods found in literature. Carbon formation rate and carbon weight gain as a function of time at various temperatures and methane partial pressures were studied, and the kinetics of CMK-3 and DUT-19 as catalysts for methane decomposition were investigated. Arrhenius energy values of 187 kJ/mol for CMK-3 and 196 kJ/mol for DUT-19 with a reaction order of 0.5 were obtained for both catalysts. Results show that carbon deposition on the catalyst during the reaction lead to catalyst deactivation with significant surface modification. Scanning electron microscope studies of fresh and deactivated catalyst samples show the blocking of catalyst pores and the formation of agglomerates on the outer surface of the catalyst during the course of reaction. DUT-19 catalytically outperforms CMK-3 because of a lower threshold temperature, higher surface area, and higher pore volume. These results show that ordered mesoporous carbons are promising catalysts for methane decomposition.     

Remarkable effect of ordered mesoporous carbon support in tantalum oxide-catalyzed selective epoxidation of cyclooctene

The olefin epoxidation is one of the most important reactions in chemical industry. Metal oxide supports often cause drawbacks in catalytic activity and selectivity, which has been overcome by introducing hydrophobic organic groups onto the oxide supports. The present study utilizes ordered mesoporous carbon (CMK-3 and CMK-1) as structurally defined hydrophobic catalyst support. Well-dispersed tantalum oxides supported on the ordered mesoporous carbon were prepared. Their application in catalytic epoxidation of cyclooctene demonstrates that the tantalum oxide catalysts on the ordered mesoporous carbon supports show higher performances than those of the catalysts supported on activated carbon and ordered mesoporous silica SBA-15.     

Synthesis of recyclable catalyst-sorbent Fe/CMK-3 for dry oxidation of phenol

The magnetic mesoporous material Fe/CMK-3 acting as a catalyst-sorbent was synthesized by using ordered mesoporous carbon CMK-3 as the supporter, Fe(NO₃)₃ as the iron source, and glycol as the reducing agent. The samples synthesized were characterized by powder X-ray diffraction (XRD), N₂ adsorption-desorption, scanning electron microscope (SEM) and transmission electron microscopy (TEM). The results show that the prepared Fe/CMK-3 preserved the ordered mesoporous structure of CMK-3, and magnetic species was mainly Fe₃O₄, which was dispersed inside channels of CMK-3 as nanoparticles with the diameter of around 10 nm. The adsorption and catalytic dry oxidation efficiency of the prepared Fe/CMK-3 were determined. The results also show that Fe/CMK-3 had good adsorption performance of phenol in aqueous solution and could be easily separated from water and recycled due to its ferromagnetic nature. Iron oxides supported on CMK-3 were excellent catalysts for dry oxidation of phenol. After 15 adsorption-catalytic oxidation cycles, the phenol adsorption capacity of Fe/CMK-3 only decreased a little, suggesting the good practicality. Combined thermogravimetry and mass spectrum (TG-MS) instrument was used to investigate the catalytic oxidation of phenol on Fe/CMK-3 and the ignition characteristics of the catalyst-sorbent. The supported Fe₃O₄ was found to be not only the magnetic component but also the active catalyst for the oxidation of phenol. The adsorbed phenol could be oxidized into CO₂ and H₂O at 220 °C at which no obvious phenol desorption or CMK-3 ignition occurred.     

Synthesis of higher alcohols from syngas over K/Co/β-Mo2C catalysts

K/Co/β-Mo₂C catalysts were prepared and tested for higher alcohols (C₂₊OH) synthesis (HAS). The catalysts exhibited high catalytic activity and selectivity to C₂₊OH. The effect of Co/Mo molar ratio in the catalysts upon the catalytic performance of HAS was investigated and the best one was at Co/Mo molar ratio of 1/8–1/6. It could be concluded that the Co promoter exerted strong promotion for carbon chain growth, especially for the stage of C₁OH to C₂OH. The XPS spectra revealed that there was a strong synergistic interaction between Co and Mo, and it depended strongly on the Co/Mo molar ratio. The new phases “Co₃Mo₃C” and “Co₂C” formed over Co promoted K/β-Mo₂C catalysts, which might be responsible for the high activity of higher alcohols and hydrocarbons synthesis, respectively.     

Synthesis of polyaniline/mesoporous carbon nanocomposites and their application for CO<Subscript>2</Subscript> sorption

Ordered mesoporous carbons (OMC), were synthesized by nanocasting using ordered mesoporous silica as hard templates. Ordered mesoporous carbons CMK-1 and CMK-3 were prepared from MCM-48 and SBA-15 materials with pore diameters of 3.4 nm and 4.2 nm, respectively. Mesoporous carbons can be effectively modified for CO₂ adsorption with amine functional groups due to their high affinity for CO₂. Polyaniline (PANI)/mesoporous carbon nanocomposites were synthesized from in-situ polymerization by dissolving OMC in aniline monomer. The polymerization of aniline molecules inside the mesochannels of mesoporous carbons has been performed by ammonium persulfate. The nanocomposition, morphology, and structure of the nanocomposite were investigated by nitrogen adsorption-desorption isotherms, Fourier Transform Infrared (FT–IR), X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and thermo gravimetric analysis (TGA). CO₂ uptake capacity of the mesoporous carbon materials was obtained by a gravimetric adsorption apparatus for the pressure range from 1 to 5 bar and in the temperature range of 298 to 348 K. CMK-3/PANI exhibited higher CO₂ capture capacity than CMK-1/PANI owing to its larger pore size that accommodates more amine groups inside the pore structure, and the mesoporosity also can facilitate dispersion of PANI molecules inside the pore channels. Moreover, the mechanism of CO₂ adsorption involving amine groups is investigated. The results show that at elevated temperature, PANI/mesoporous carbon nanocomposites have a negligible CO₂ adsorption capacity due to weak chemical interactions with the carbon nanocomposite surface.     

Activated Carbon‐Supported Mo‐Co‐K Sulfide Catalysts for Synthesizing Higher Alcohols from CO2

Activated carbon‐supported Mo‐Co‐K sulfide catalysts, prepared by stepwise impregnation, were used in the synthesis of higher alcohols via CO₂ hydrogenation. The catalysts with varying Mo contents and defined K/Mo and Co/Mo molar ratios exhibited relatively high CO₂ conversions and high selectivity to total alcohols and C₂₊ alcohols. Moreover, the influence of calcination conditions on the sulfidation states and catalytic performance was studied. The surface sulfur runoff of the supported catalysts can be effectively suppressed by online calcination. As a result, the selectivity to total alcohols and C₂₊ alcohols can be improved.     

Enhanced liquid phase catalytic hydrodechlorination of 2,4-dichlorophenol over mesoporous carbon supported Pd catalysts

Supported Pd catalysts on ordered mesoporous carbon (OMC) and activated carbon (AC) were prepared and their catalytic behavior for the liquid phase catalytic hydrodechlorination (HDC) of 2,4-dichlorophenol was investigated. In comparison with Pd/AC, Pd particles of Pd/OMC were effectively confined in the mesopores of OMC, resulting in high Pd dispersion and Pd²⁺ content. Accordingly, Pd/OMC exhibited higher catalytic activity than Pd/AC. Moreover, increasing catalyst reduction temperature lowered the catalytic activities and favored stepwise HDC of 2,4-dichlorophenol.     

Pd/CMK-3的合成及其在Suzuki-Miyaura碳-碳偶联反应中的应用

利用介孔二氧化硅（SBA-15）为模板、蔗糖为碳源,制备了有序介孔碳材料CMK-3,然后以CMK-3为载体,利用浸渍还原法得到介孔碳负载Pd纳米粒子的复合催化剂（Pd/CMK-3）,通过XRD、TEM以及氮气吸附-脱附等手段对催化剂的微结构和组分进行分析,结果表明CMK-3为有序介孔结构,孔径约为5nm,Pd/CMK-3保留了介孔结构,且孔道中负载有不同尺寸的Pd粒子。应用于无配体催化的Suzuki-Miyaura相似文献   

Preparation of mesoporous silica replica using ordered mesoporous carbon by vapor phase transport of silica source

A new vapor phase transport (VPT) technique to prepare an inverse silica replica of an ordered mesoporous carbon was developed. Tetraethyl orthosilicate (TEOS) was infiltrated in mesoporous carbon CMK-3 as the hard template at 180 °C for 48 h under an autogenous pressure in an autoclave in the presence of water. The samples obtained by removal of CMK-3 retained structural regularity of CMK-3 with little shrinkage of framework, which were characterized by SAXRD, N₂ adsorption, TG-DTA, and SEM. Influence of preparation temperature on the loading amount of silica was investigated. The multi-step replication process was monitored by characterizing the replicated materials as well as intermediate composites.     

SO3H-functionalized mesoporous carbon/silica composite with a spherical morphology and its excellent catalytic performance for biodiesel production

Mesoporous carbon/silica composites functionalized with –SO₃H groups were prepared via polymerization and carbonization of glucose into mesoporous silica SBA-15 and a followed sulfonation by sulphuric acid. These composites were characterized by powder X-ray diffraction, N₂ adsorption–desorption and transmission electron microscopy, which suggested the preservation of ordered mesoporous structure, as well as a novel spherical morphology. The result of fourier transform infrared spectroscopy indicated the successful modification of –SO₃H groups and the acidity of catalysts was determined by an indirect titration method. The composite with 40 % carbon loading possessing the highest acidity in synthesized catalysts and the ordered mesoporous structure without pore blocking exhibited a remarkable catalytic activity for biodiesel production. Experimental parameters including the carbon loading, molar ratio of reactants, reaction time and reaction temperature were optimized. In addition, a superior recycling property was exhibited after five consecutive cycles.     

Platinum and platinum-ruthenium nanoparticles supported on ordered mesoporous carbon and their electrocatalytic performance for fuel cell reactions

Highly ordered meso-porous carbon, denoted CMK-3 was synthesized by using mesoporous silicates, SBA-15 as the starting templating materials. The ordered mesoporous carbon was loaded with platinum and platinum-ruthenium nanoparticles using alternative synthesis techniques. The metal loaded ordered mesoporous carbon powders were characterized by transmission electron microscopy (HRTEM), energy dispersive X-ray analysis (EDX), X-ray diffraction, and nitrogen adsorption isotherm experiments. Micrometer-scale and centimeter-scale electrodes containing the mesocarbon/nanometal electrocatalysts were tested for some typical fuel cell reactions. While the nanometal/mesocarbon catalysts have well-defined and uniform properties in the nanometer scale, they have mixed electrocatalytic performance. A synthesized Pt/mesocarbon electrocatalyst outperformed a commercial electrocatalyst for oxygen reduction on a gas-diffusion electrode. The Pt-Ru/mesocarbon electrocatalyst synthesized, however, was not as effective for methanol oxidation.     

Improving the electrocapacitive properties of mesoporous CMK-5 carbon with carbon nanotubes and nitrogen doping

Nitrogen-containing carbon composite materials composed of mesoporous carbon CMK-5 and carbon nanotubes (CNTs) were prepared by the chemical vapor deposition method with Fe(NO₃)₃-impregnated SBA-15 as template and pyridine as the carbon precursor. The Fe nanoparticles confined in the channels of SBA-15 induced the formation of mesoporous carbon characteristic of CMK-5, whereas Fe particles homogeneously dispersed on the external surface of SBA-15 served as catalysts for CNTs growth. The contents of CNTs, the N doping level and the microstruture of the carbon composite were closely related to the initial Fe/Si atomic ratio in SBA-15 template. Incorporation of CNTs in the composite was found to substantially reduce the electric resistance, leading to the composite materials exhibiting excellent rate-performance. A maximum specific capacitance of 208 F/g and a power density of 10 kW/kg were achieved in 6.0 mol/L KOH aqueous electrolyte when these carbon composites were applied as supercapacitor electrodes. Moreover, the composite electrode also exhibited good electrochemical stability with no capacitance loss after 1000 cycles of galvanostatic charge-discharge process.     

Catalytic hydrogenation of carbon monoxide over silica-supported Ir-Mo-Rh catalyst

We present here some results on Ir-Mo-Rh metallic catalysts for the synthesis of C₂-C₄ alcohols from syngas. It was found that Ir-Mo-Rh supported on silica containing small amounts of Rh exhibited much higher activity for CO hydrogenation than Ir-Mo bimetallic catalyst. The selectivity to various alcohols did not change very much upon the addition of Rh. The activity was greatly affected by the impregnation procedure of the metals in the catalyst preparation.     

Graphitic mesoporous carbon as a support of promoted Rh catalysts for hydrogenation of carbon monoxide to ethanol

Graphitic mesoporous carbon (GMC), prepared through high-temperature graphitization of soft-templated amorphous mesoporous carbon (AMC), was used as the support for Mn, Li, and Fe triple-promoted Rh catalysts for CO hydrogenation to ethanol. The use of GMC results in C₂H₅OH selectivity and formation rate comparable to nonporous SiO₂ support along with a significant inhibition on the formation of undesired CH₄ and light hydrocarbons at the expense of appreciable amounts of CO₂ produced. The better catalytic performance of promoted-Rh/GMC than those supported on other carbon allotropes (AMC and non-porous graphitic carbon black) seems to be associated with the specific graphitic structure and mesoporosity of GMC. The surface modification of GMC by wet oxidation leads to considerable increases in C₂H₅OH selectivity and formation rate. The modified GMC as a support shows substantially greater CO₂-free selectivity for C₂H₅OH than the SiO₂.     

Synthesis of nickel catalysts supported on Zr-doped ordered mesoporous Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and their catalytic performance for low-temperature CO<Subscript>2</Subscript> reforming of CH<Subscript>4</Subscript>

A series of Zr-doped ordered mesoporous Al₂O₃ with various Zr contents were synthesized by evaporation-induced self-assembly strategy and the Ni-based catalysts supported on these Al₂O₃ materials were prepared by impregnation method. These catalysts with large specific surface area, big pore volume, uniform pore size possess excellent catalytic performance for the low-temperature carbon dioxide reforming of methane. The activities of these catalysts were tested in carbon dioxide reforming of methane reaction with temperature increasing from 500 to 650?°C and the stabilities of these catalysts were evaluated for long time reaction at 650?°C. It was found that when Zr/(Zr?+?Al) molar ratio?=?0.5%, the Ni/0.5ZrO₂–Al₂O₃ catalyst showed the highest activity, and exhibited superior stabilization compared to the Ni-based catalyst supported on traditional ordered mesoporous Al₂O₃. The “confinement effect” from mesoporous channels of alumina matrix is helpful to stabilize the Ni nanoparticles. As a promoter, Zr could stabilize the ordered mesoporous framework by reacting with Al₂O₃ to form ZrO₂–Al₂O₃ solid solution. Since ZrO₂ enhances the dissociation of carbon dioxide, more oxygen intermediates are given to remove the carbon formed during the reaction.     

Supercapacitive behavior of mesoporous carbon CMK-3 in calcium nitrate aqueous electrolyte

Calcium nitrate Ca(NO₃)₂ aqueous solution was found to be an effective aqueous electrolyte for a supercapacitor using ordered mesoporous carbon as the electrode materials. The supercapacitive behavior of ordered mesoporous carbon CMK-3 electrode in Ca(NO₃)₂ aqueous electrolyte was investigated utilizing cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charge/discharge measurements. CMK-3 electrode shows excellent supercapacitive behavior with wide voltage window, high specific gravimetric capacitance and satisfactory electrochemical stability in Ca(NO₃)₂ aqueous electrolyte. The specific gravimetric capacitance of CMK-3 electrode in Ca(NO₃)₂ aqueous electrolyte reaches 210 F g^?1 at a current density of 1 A g^?1, which is higher than that in conventional aqueous electrolytes NaNO₃ and KOH solution about 40% and 54%, respectively. The high charge density of the electric double layer formed at the interface of the CMK-3 electrode and Ca(NO₃)₂ aqueous electrolyte and the pseudo-capacitive effect originating from the oxygen groups on the surface of CMK-3 were believed to respond for the excellent supercapacitive behavior of CMK-3 electrode in Ca(NO₃)₂ aqueous electrolyte.     

Impact of framework structure of ordered mesoporous carbons on the performance of supported Pt catalysts for oxygen reduction reaction

Ordered mesoporous carbons (OMCs) are investigated as support materials for Pt catalysts for oxygen reduction reaction (ORR). Three types of OMCs (CMK-3, CMK-3G, and CMK-5) are prepared by a nanocasting method using ordered mesoporous silica, SBA-15, as a template. These OMCs with the same hexagonal mesostructure have different carbon frameworks and graphiticity, which can affect their surface area and microporosity. Pt nanoparticles with an average size of 1 nm are uniformly supported on the three OMCs and Ketjenblack® and their electrochemical performance and durability are evaluated. Pt/CMK-3G exhibits the highest electrochemically active surface area, kinetic current density, mass activity, and half-wave potential, whereas Pt/CMK-3 shows the lowest values. Pt/CMK-3G also shows the highest ORR activity after an accelerated durability test, with a minimal shift in half-wave potential. The higher ORR activity of Pt/CMK-3G is attributed to the formation of highly crystalline Pt particles as well as its highly graphitic, crystalline carbon structure, which causes the weak adsorption of surface oxide and a strong interaction between the Pt particles and the support. Moreover, we can establish that the mass activity of the catalysts is nearly inversely proportional to the micropore volume of the carbon supports.     

Characterization and catalytic performance of poly(4-vinylpyridine) supported on mesoporous carbon: comparison with poly(4-vinylpyridine) supported on mesoporous silica

In this study, the synthesis of poly(4-vinylpyridine) (P4VP) supported on mesoporous carbon (CMK-3) by in situ polymerization of 4-vinylpyridine in the presence of CMK-3 has been investigated. The structural properties of the P4VP/CMK-3 were investigated by FT-IR, XRD, BET, TGA, SEM and TEM techniques. The catalytic activity of this new heterogeneous basic catalyst was tested for Knoevenagel reaction. Excellent yields at room temperature in aqueous media and solvent-free conditions were obtained. The catalytic activity of this purely organic hybrid catalyst was compared with P4VP/SBA-15 to clarify the advantages of mesoporous carbon on mesoporous silica as support. The results showed that the stability of P4VP/CMK-3 was excellent and could be reused 10 times without much loss of activity in Knoevenagel reaction. Surprisingly, the composite prepared by mesoporous carbon showed much higher activity than that of P4VP/SBA-15. This unique result opens new perspectives for application of mesoporous carbons as structurally defined hydrophobic catalyst support in catalytic reactions.     

磺酸化碳材料负载Ru催化剂催化纤维素水解/加氢反应

采用纤维素衍生碳、活性炭和介孔碳材料CMK-3为不同碳源前驱体,在不同磺酸化条件下制备磺酸化碳材料负载Ru的双功能催化剂,并用FTIR光谱、XRD、元素分析、热重分析、N₂物理吸附 脱附进行了表征,考察了其对纤维素加氢反应的催化活性。结果表明：相比于纤维素衍生化碳,活性炭和介孔碳CMK-3为碳源经过磺酸化后制备的催化剂具有较强的结合-SO₃H的能力和较高的催化活性,对多元醇具有良好的选择性,170 ℃下反应10 h六元醇的收率可高达84.0%。在循环使用时,磺酸化活性炭负载Ru催化剂催化活性有所降低,但可以保持对多元醇的选择性;而磺酸化介孔碳负载Ru催化剂存在少量S流失,转化率基本不变,但产物的选择性有所降低。     

Controlling the textural parameters of mesoporous carbon materials

The mesoporous carbon materials prepared by inorganic templating technique using mesoporous silica, SBA-15 as a template and sucrose as a carbon source, have been systematically investigated as a function of sucrose to mesoporous silica composition, with a special focus on controlling the mesoporous structure, surface morphology and the textural parameters such as specific surface area, specific pore volume and pore size distribution. All the materials have been unambiguously characterized by XRD, N₂ adsorption–desorption isotherms, high-resolution transmission electron microscopy, high-resolution field emission scanning electron microscopy, and Raman spectroscopy. It has been found that the porous structure, morphology and the textural parameters of the mesoporous carbons materials, CMK-3-x where x represent the sucrose to silica weight ratio, can be easily controlled by the simple adjustment of concentration of sucrose molecules. It has also been found that the specific surface area of the mesoporous carbon materials systematically increases with decreasing the sucrose to silica weight ratio. Moreover, the specific pore volume of the materials increases from 0.57 to 1.31 cm³/g with decreasing the sucrose to silica weight ratio from 5 to 1.25 and then decreases to 1.23 cm³/g for CMK-3-0.8. HRTEM and HR-FESEM also show a highly ordered pore structure and better surface morphology for CMK-3-1.25 as compared to other materials prepared in this study. Thus, it can be concluded that the sucrose to silica weight ratio of 1.25 is the best condition to prepare well ordered mesoporous carbon materials with good textural parameters, pore structure and narrow pore size distribution.