Chemical activation of mesoporous carbon with ultrahigh pore volume for highly supported adsorption of CO<Subscript>2</Subscript>

A novel mesoporous carbon (AMC850) with worm-like mesoporosity, very large BET surface area (2935 m²/g), and ultrahigh pore volume of 3.41 cm³/g was facilely synthesized from etching of the pristine mesoporous carbon (MC850) with sodium amide (NaNH₂). The mesoporosity in the synthesized AMC850 was significantly expanded in comparison with pristine mesoporous carbon. The synthesized AMC850acts as an efficient support, could accommodate much more pentaethylenehexamine (PEHA) in comparison with the pristine MC850, giving PEHA@AMC850 composites. The resultant PEHA@AMC850 showed much improved property for the selective capture of CO₂ in comparison with AMC850 (2.02 mmol/g vs. 0.73 mmol/g, at 75 °C). Thus, the PEHA@AMC850 composites showed promising application in the selective capture of CO₂ from flue gas.     

Deposition of diamond from a plasma jet with phenol as the carbon source

The deposition of diamond on a molybdenum substrate was studied in an Ar–H₂ plasma jet adding phenol (C₆H₅OH) as a carbon source and was compared with adding benzene (C₆H₆) to examine the effect of OH species on diamond deposition. Better faceted and larger crystal size diamond was deposited from the Ar–C₆H₅OH–H₂ plasma jet than from the Ar–C₆H₆–H₂ plasma jet. Furthermore, the amount of co-deposited graphite and/or amorphous carbon in the deposit from the Ar–C₆H₅OH–H₂ plasma jet was smaller than that in the deposit from the Ar–C₆H₆–H₂ plasma jet. At the beginning of the exposure to the Ar–C₆H₅OH–H₂ plasma jet, in which OH radicals were identified, the surface of the substrate was slightly oxidized. Oxide formation on the surface of the substrate by reaction with OH radicals would contribute to the purification and increase of crystal size in the diamond deposition with an Ar–C₆H₅OH–H₂ plasma jet.     

One-step purification of ethylene from acetylene and carbon dioxide by ultramicroporous carbons

The one-step adsorptive separation of high-purity ethylene (C₂H₄) from a ternary gas mixture (C₂H₂/C₂H₄/CO₂) is challenging and has not been reported on porous carbons. Herein, we report camphor seeds husk-derived ultramicroporous carbons (CSHs) show high affinities toward acetylene (C₂H₂) and carbon dioxide (CO₂) over C₂H₄. The optimized CSH-2-700 with high heteroatom contents and centered pore size distributions shows high C₂H₂ adsorption capacity (2.24 mmol g⁻¹) and record ideal adsorbed solution theory (IAST) C₂H₂/C₂H₄ selectivity (10.2) among one-step C₂H₄ purification adsorbents. Meanwhile, CSH carbons are the only carbon adsorbents that preferentially adsorb CO₂ over C₂H₄, with a CO₂/C₂H₄ selectivity of 1.9 under ambient conditions. Furthermore, dynamic breakthrough experiments verified its feasibility for one-step C₂H₄ purification from a three-component C₂H₂/C₂H₄/CO₂ gas-mixture.     

Mesoporous silica-supported chromium catalyst: Characterization and excellent performance in dehydrogenation of propane to propylene with carbon dioxide

Nonordered mesoporous molecular sieves MSU-x supported chromium catalysts (Cr/MSU-x) were prepared and characterized with X-ray diffraction, diffuse reflectance UV–vis, and H₂-temperature programmed reduction techniques. Excellent results in dehydrogenation of propane to propylene with carbon dioxide (CO₂) over Cr/MSU-x, 36.8% of propane conversion with 89.1% of propylene selectivity, were obtained. Lower Cr loading results in formation of Cr species with higher oxidation state, whereas higher Cr loading leads to bulk chromium oxide (Cr₂O₃) crystal on catalyst surface. The active sites of the catalysts and the promoting effect of mesoporous MSU-x as support were also discussed.     

Formation and gasification of carbon deposits on NiSiO2 catalysts

The deposition of carbon from CH₄ and CO on $\text{Ni}\text{SiO}{}_2$ catalysts was studied in pulse-flow experiments as well as volumetrically with a low-field magnetic permeameter. It was found that carbon, deposited from CH₄ according to: CH₄ → C + 4H, gave rise to the formation of nickel carbide, Ni₃C, only at the surface of the nickel particles (T< 300 °C). However, carbon, deposited from CO according to: 2CO → C + CO₂, led to the formation of a bulk nickel carbide as well as dissolution of carbon interstitially. The reactivity of the carbon thus deposited was studied with both H₂ and H₂O. The rate of reaction with hydrogen appeared to be a function of temperature: the rate passed through a maximum at 200 °C and dropped steeply above 300 °C. The only product of the reaction was CH₄. The reaction with H₂O produced besides CH₄, CO₂ and (at low carbon surface coverages) H₂.     

Palladium Catalysts for Fatty Acid Deoxygenation: Influence of the Support and Fatty Acid Chain Length on Decarboxylation Kinetics

Supported metal catalysts containing 5?wt% Pd on silica, alumina, and activated carbon were evaluated for liquid-phase deoxygenation of stearic (octadecanoic), lauric (dodecanoic), and capric (decanoic) acids under 5?% H₂ at 300?°C and 15?atm. On-line quadrupole mass spectrometry (QMS) was used to measure CO?+?CO₂ yield, CO₂ selectivity, H₂ consumption, and initial decarboxylation rate. Post-reaction analysis of liquid products by gas chromatography was used to determine n-alkane yields. The Pd/C catalyst was highly active and selective for stearic acid (SA) decarboxylation under these conditions. In contrast, SA deoxygenation over Pd/SiO₂ occurred primarily via decarbonylation and at a much slower rate. Pd/Al₂O₃ exhibited high initial SA decarboxylation activity but deactivated under the test conditions. Similar CO₂ selectivity patterns among the catalysts were observed for deoxygenation of lauric and capric acids; however, the initial decarboxylation rates tended to be lower for these substrates. The influence of alkyl chain length on deoxygenation kinetics was investigated for a homologous series of C₁₀?CC₁₈ fatty acids using the Pd/C catalyst. As fatty acid carbon number decreases, reaction time and H₂ consumption increase, and CO₂ selectivity and initial decarboxylation rate decrease. The increase in initial decarboxylation rates for longer chain fatty acids is attributed to their greater propensity for adsorption on the activated carbon support.     

Structural characterization of carbon nanofibers formed from different carbon-containing gases

Catalytically grown carbon nanofibers, a novel mesoporous carbon material for catalysis, were synthesized by the decomposition of carbon-containing gases (CH₄, C₂H₄ or CO) over supported nickel-iron alloy and unsupported iron. It was shown that the structures of as-synthesized and modified CNFs, including the arrangement of the graphenes in CNF, and the crystallinity and texture of CNF depended on the catalyst composition and the type of carbon-containing gas. Three types of CNFs with different microstructures were obtained: platelet CNF (Fe–CO), fishbone CNF (supported Ni–Fe alloy-CH₄, C₂H₄ or CO) and tubular CNF (supported Ni–CO). All the CNFs were mesoporous carbon materials possessing relatively high surface areas (86.6–204.7 m²/g) and were highly graphitic. Purification with acid-base treatments or high temperature treatment removed the catalyst residue without changing the basic structures of the CNFs. However, annealing significantly decreased their surface areas through the formation of loop-shaped ends on the CNF surfaces. Oxidative modification in the gas and liquid phases changed the structures only slightly, except for oxidation in air at 700 °C. The structures and textures were studied using SEM, TEM, XRD, BET and TGA.     

Porous MoxCy/SiO2 Material for CO2 Hydrogenation

The synthesis and characterization of an inexpensive porous Mo_xC_y/SiO₂ material is presented, which was obtained by mixing ammonium hexamolybdate, sucrose, and a mesoporous silica (SBA-15), with a subsequent heat treatment under inert atmosphere. This porous material presented a specific surface area of 170 m²/g. The catalytic behavior in CO₂ hydrogenation was compared with that of Mo₂C and α-MoC_1?x obtained from ammonium hexamolybdate and sucrose, using different Mo/C ratios. CO₂ hydrogenation tests were performed at moderate (100 kPa) and high pressures (2.0 MPa), and it was found that only CO, H₂O and CH₄ are formed at moderate pressures by the three materials, while at higher pressures, methanol and hydrocarbons (C₂H₆, C₃H₈) are also obtained. Differences in selectivity were observed at the high pressure tests. Mo₂C presented higher selectivity to CO and methanol compared with MoC_1?x, which showed preferential selectivity to hydrocarbons (CH₄, C₂H₆). The porous Mo_xC_y/SiO₂ material showed the highest CO₂ hydrogenation activity at high temperatures (270 and 300 °C), being a promising material for the conversion of CO₂ to CO and CH₄.

     

Ultrathin carbon molecular sieve membrane for propylene/propane separation

Ultrathin (down to 300 nm), high quality carbon molecular sieve (CMS) membranes were synthesized on mesoporous γ‐alumina support by pyrolysis of defect free polymer films. The effect of membrane thickness on the micropore structure and gas transport properties of CMS membranes was studied with the feed of He/N₂ and C₃H₆/C₃H₈ mixtures. Gas permeance increases with constant selectivity as the membrane thickness decreases to 520 nm. The 520‐nm CMS membrane exhibits C₃H₆/C₃H₈ mixture selectivity of ～31 and C₃H₆ permeance of ～1.0 × 10^?8 mol m^?2 s^?1 Pa^?1. Both C₃H₈ permeance and He/N₂ selectivity increase, but the permeance of He, N₂, and C₃H₆ and the selectivity of C₃H₆/C₃H₈ decrease with further decrease in membrane thickness from 520 to 300 nm. These results can be explained by the thickness‐dependent chain mobility of the polymer film which yields thinner final CMS membranes with reduction in pore size and possible closure of C₃H₆‐accessible micropores. © 2015 American Institute of Chemical Engineers AIChE J, 62: 491–499, 2016     

Organometallics derived (Pd + Ln)/SiO2 catalysts for the reactions of synthesis gas conversion

C₃H₆ hydroformylation and CH₃OH synthesis on organometallics derived (Pd + Ln)/ SiO₂ and Pd/SiO₂ catalysts have been studied. The activity and selectivity towards methanol in CO + H₂ reaction were observed to increase for all the modified catalysts while both the hydroformylation activity and selectivity towards oxygenates in C₃H₆ hydroformylation decreased for the catalysts in comparison to those of Pd/SiO₂. The FTIR, TPD data and characteristic catalytic properties of the catalysts studied allow to suggest that C₃H₆ hydroformylation on (Pd + Ln)/SiO₂ catalysts occurs on monometallic Pd clusters without participation of mixed active sites and CO complexes activated thereon.     

A high CO2 permselective mesoporous silica/carbon composite membrane for CO2 separation

Ordered mesoporous silica/carbon composite membranes with a high CO₂ permeability and selectivity were designed and prepared by incorporating SBA-15 or MCM-48 particles into polymeric precursors followed by heat treatment. The as-made composite membranes were characterized by high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD) and N₂ adsorption, of which the gas separation performance in terms of gas permeability and selectivity were evaluated using the single gas (CO₂, N₂, CH₄) and gas mixtures (CO₂/N₂ and CO₂/CH₄, 50/50 mol.%). In comparison to the pure carbon membranes and microporous zeolite/C composite membranes, the as-made mesoporous silica/C composite membranes, and the MCM-48/C composite membrane in particular, exhibit an outstanding CO₂ gas permeability and selectivity for the separation of CO₂/CH₄ and CO₂/N₂ gas pairs owing to the smaller gas diffusive resistance through the membrane and additional gas permeation channels created by the incorporation of mesoporous silicas in carbon membrane matrix. The channel shape and dimension of mesoporous silicas are key parameters for governing the gas permeability of the as-made composite membranes. The gas separation mechanism and the functions of porous materials incorporated inside the composite membranes are addressed.     

Highly selective oxidation of alcohols catalyzed by Cu(II)-Schiff base-SBA-15 with hydrogen peroxide in water

An efficient catalyst for selective oxidation of alcohols was prepared by grafting the Cu(II) Schiff base complex onto the channels of mesoporous silica material SBA-15. The characterizations illustrated that the functionalized SBA-15 maintained the primary hexagonally ordered mesoporous structure, and the Cu(II) Schiff base complexes were bonded inside the mesoporous channels of SBA-15. The selective oxidation of benzyl alcohol was carried out in water phase with hydrogen peroxide. The C₆H₅CH₂OH conversion could reach 98.5 % with 100 % of the selectivity to C₆H₅CHO under the optimum conditions. The catalyst could also react well on the selective oxidation of other primary alcohols.     

碱性嫁接型离子液体催化二氧化碳环加成反应

采用后嫁接法将不同量的1-甲基-3-丙基(三乙氧基硅基)咪唑的氢氧化物(［Smim］OH)嫁接到介孔硅胶(SiO₂)上,采用傅里叶变换红外光谱、元素分析、硅核磁共振及热重分析等技术对所制备的材料进行表征。在无溶剂、温和的条件下,将碱性嫁接型离子液体用于CO₂与环氧丙烷(PO)合成碳酸丙烯酯(PC)的环加成反应来考察其催化活性。结果表明,离子液体［Smim］OH成功地以共价键嫁接到介孔硅胶上得到碱性嫁接型离子液体(GILs),但不同量的［Smim］OH嫁接程度有所不同;在优化条件下,PO的转化率为99.5%,选择性为100%。反应后催化剂经过滤即可分离回收利用,且多次使用仍保持较高的反应活性。     

Increasing carbon utilization in Fischer-Tropsch synthesis using H2-deficient or CO2-rich syngas feeds

Fischer-Tropsch technology has become a topical issue in the energy industry in recent times. The synthesis of linear hydrocarbon that has high cetane number diesel fuel through the Fischer-Tropsch reaction requires syngas with high H₂/CO ratio. Nevertheless, the production of syngas from biomass and coal, which have low H₂/CO ratios or are CO₂ rich may be desirable for environmental and socio-political reasons. Efficient carbon utilization in such H₂-deficient and CO₂-rich syngas feeds has not been given the required attention. It is desirable to improve carbon utilization using such syngas feeds in the Fischer-Tropsch synthesis not only for process economy but also for sustainable development. Previous catalyst and process development efforts were directed toward maximising C₅₊ selectivity; they are not for achieving high carbon utilization with H₂-deficient and CO₂-rich syngas feeds. However, current trends in FTS catalyst design hold the potential of achieving high carbon utilization with wide option of selectivities. Highlights of the current trends in FTS catalyst design are presented and their prospect for achieving high carbon utilization in FTS using H₂-deficient and CO₂-rich syngas feeds is discussed.     

Nanoporous carbon membrane for gas separation

A novel method for production of nanoporous carbon membranes by carbonization of a polymer latex is described. The estimated pore size of the membrane is between 5.0 and 5.5 Å (diameter). The membrane can separate H₂ from mixtures with CO₂, CH₄, C₂H₆ and C₃ H₈ by selective adsorption and surface diffusion of the larger components. A moderate to high selectivity of the adsorbing components can be achieved through the membrane while maintaining fairly high permeabilities for these components even at a moderate feed-gas pressure. The membrane can be used to enrich H₂ from a stream containing these components.     

Hydrogenation of carbon dioxide on cobalt catalysts – activation,deactivation, influence of carbon monoxide

A batch reactor directly combined with an ultrahigh vacuum apparatus, which is equipped with facilities for catalyst preparation and Auger electron spectroscopy, was used to answer some questions which had arisen in recent studies concerning carbon dioxide hydrogenation on pure metallic and supported Co catalysts. Both oxygen incorporated during oxidation/reduction cycles and carbon deposited when CO₂ is hydrogenated penetrate deep into the bulk. This kind of carbon can easily be hydrogenated. CO strongly hinders the reduction of the oxidized Co surface in the H₂/CO₂ reaction mixture (4 : 1). CO hydrogenation is favoured over CO₂ hydrogenation and leads to a higher percentage of C₂ to C₄ hydrocarbons as compared with CH₄ formation.     

The Role of Support Acidity in the Selective Catalytic Reduction of NO by C3H6 Under Lean-Burn Conditions

Mechanical mixtures consisting of a catalyst (Pt/SiO₂ or Pt/SiO₂–Al₂O₃) and supports of varying acidity (hydrotalcite, SiO₂, SiO₂–Al₂O₃, and ZSM-5 zeolite) were tested for the selective reduction of NO by C₃H₆. A certain degree of support acidity appears to favour N₂ selectivity, but if there are too many acid sites, carbon deposition becomes extensive and leads to catalyst deactivation.     

Hydrogenation of carbon dioxide over alumina supported Fe-K catalysts

The hydrogenation of CO₂ has been studied over Fe/alumina and Fe-K/alumina catalysts. The addition of potassium increases the chemisorption ability of CO₂ but decreases that of H₂. The catalytic activity test at high pressure (20 atm) reveals that remarkably high activity and selectivity toward light olefins and C₂₊ hydrocarbons can be achieved with Fe-K/alumina catalysts containing high concentration of K (K/Fe molar ratio = 0.5, 1.0). In the reaction at atmospheric pressure, the highly K-promoted catalysts give much higher CO formation rate than the unpromoted catalyst. It is deduced that the remarkable catalytic properties in the presence of K are attributable to the increase in the ability of CO₂ chemisorption and the enhanced activity for CO formation, which is the preceding step of C₂₊ hydrocarbon formation.     

Direct synthesis of diphenyl carbonate by mediated electrocarbonylation of phenol at Pd-supported activated carbon anode

Mediated electrocarbonylation of phenol to diphenyl carbonate (DPC) at a PdCl₂-supported activated carbon anode in 1 atm CO at 298 K was studied. A dry CH₂Cl₂ or CH₃CN solvent and a galvanostatic electrolysis of 1 mA were necessary for formation of DPC, while the addition of a base and a supporting electrolyte was also essential. A combination of triethylamine (Et₃N) and tetrabutylammonium perchlorate (Bu₄NClO₄) was suitable in various combinations. The addition of 2 equiv. of Et₃N to the electrolyte (C₆H₅OH/Bu₄NClO₄/CH₂Cl₂) at 1-h intervals was more efficient in the formation of DPC than a single initial addition of the same amount of Et₃N. The yield of DPC was 130% based on Pd and its current efficiency (CE) was 42% for 6 h. The CE of the CO₂ formation was only 3%. Sodium phenoxide (PhONa) showed dual functionality as a base and supporting electrolyte. When the mediated electrocarbonylation was conducted in a C₆H₅OH/PhONa/CH₃CN electrolyte, DPC was produced in 172% yield and 40% CE for 6 h. The CE of the CO₂ formation was 10%. DPC formed continuously after a single initial addition of 4 equiv. of PhONa. Li or K phenoxide also worked as promoters for the mediated electrocarbonylation of phenol to DPC.     

Deposition of Pd into mesoporous silica SBA-15 using supercritical carbon dioxide

Pd was deposited into mesoporous silica SBA-15 using supercritical CO₂ (scCO₂). Palladium hexafluoroacetylacetonate [Pd(hfac)₂] was dissolved in scCO₂ and impregnated into the support at very mild conditions, 40 °C and 85 bar. Then the organometallic precursor was reduced with H₂ in the CO₂ mixture or, after depressurization, in pure H₂. Materials were characterized by TGA, XRD, TEM, SEM, EDX, ICP-OES and N₂-adsorption experiments. Pd nanoparticles evenly distributed into the support (1-3 mol% Pd by ICP-OES) are only obtained when the reduction is performed in pure H₂. Cluster size is limited in two dimensions by the pore size of the support but clusters grow larger with increasing impregnation time and turn into small nanowires. The catalytic activity of the Pd/SiO₂ composite material was confirmed following the reduction of 4-nitrophenol to 4-aminophenol in water by UV-vis spectroscopy.