Carbon as a support for catalysts—III glassy carbon as a support for iron

As described in the Hucke patent, glassy carbons containing not only open pores of molecular size but also pores in the transitional or macropore range can be produced from appropriate formulations. The formulation always consists of a carbon-yielding monomer, an organic to yield larger pores upon its removal once the monomer has been partially polymerized, and a polymerization catalyst. It may contain a dispersing agent, depending upon the size of the larger pores which is desired. In this study, furfuryl alcohol was the monomer. Great flexibility is shown to exist in the total surface areas of the carbons which can be produced, degree of carbon molecular sieving in the super micropores, and pore volume and pore size in the larger pores following polymerization and carbonization steps. Different ways of adding iron into the mix are explored which also can have pronounced effects on the nature of the porosity in the final carbons. Further modification is shown upon addition of potassium or boron into the mix. Carbons produced are expected to have potential as catalyst supports.     

Mixed oxides as a support for new CoMo catalysts

Interest in bifunctional catalysts, active in reactions such as hydrodesulphurisation (HDS) of hydrocarbon fractions, is growing in the last years. An improvement of CoMo/Al₂O₃ materials can be obtained by the introduction of other oxides during the sol–gel synthesis. This heavily affects the acid–base characteristics of the catalysts, while textural properties are less influenced. The catalytic performances change as well: a relationship between the density of acid sites and HDS activity has been found.     

Disordered mesoporous KIT-1 as a support for hydrodesulfurization catalysts

MoO₃ and NiO were supported on KIT-1, a new disordered mesoporous molecular sieve. MoO₃ is homogeneously dispersed as a monolayer on the support, whereas NiO tends to form small crystallites in the mesoporous channels. KIT-1 supported MoO₃ and/or NiO catalysts exhibit higher catalytic activities for thiophene hydrodesulfurization than similar MCM-41 and NaY zeolite supported catalysts, because the three-dimensional disordered network of short channels in KIT-1 reduces the risk of blockage in the catalysts and facilitates the transport of reactant and product molecules. This revised version was published online in July 2006 with corrections to the Cover Date.     

MFI zeolite as a support for automotive catalysts with reduced Pt sintering

The noble metals used as catalysts in automotive exhaust systems are subject to sintering at extreme temperatures, leading to deterioration of catalytic activity. Zeolite with the MFI (ZSM5) structure is examined as a support for Pt particulate catalysts. The MFI structure is composed of agglomerates of single-crystal zeolite with interstitial mesoporosity. Pt fixed within these mesopores is shown through high-temperature aging tests in air to be highly resistant to sintering due to the mechanical constraints on particle size imparted by the mesoporous structure. The deterioration of catalytic activity after aging is significantly lower than that for comparable γ-alumina supported catalyst.     

Miniemulsion polymers as solid support for transition metal catalysts

A pentadentate salen-type ligand was immobilized in a poly[(styrene)]-co-(butyl acrylate)] matrix by miniemulsion polymerization. The obtained polymer beads revealed a particle size of 50 nm in the dry state by transmission electron microscopy. Dynamic light scattering experiments in methanol and water showed a solvent-dependent average particle size with a mean particle diameter of up to 233 nm in methanol. These results provide valuable insights for the optimization of macromolecular oxidation catalysts and their future use as enzyme-like entities in aqueous media. The particle stability was demonstrated over a wide pH range (3-11) by gel permeation chromatography, and initial results for the metal ion binding ability were obtained.     

Porous carbon as support for iron and ruthenium catalysts

Iron and ruthenium catalysts have been supported on a porous carbon prepared by pyrolysis and activation of the copolymer Saran. For comparison, a graphitized carbon black (V3G) has also been used as support for both metals. The catalysts have been characterized by chemisorption of H₂ and CO₂ at 298 K (373 K in some cases) and by X-ray line broadening. The hydrogen chemisorption on iron catalysts was very low and increased with adsorption temperature, whereas the CO chemisorption results indicate the formation of subcarbonyl species. However, H₂ and CO uptakes led to similar dispersion values for the ruthenium catalysts. The X-ray results were in good agreement with the chemisorption results except in the case of highly dispersed Fe catalysts. The results obtained in the hydrogenation of CO indicate that in the case of Fe catalysts the highest selectivity toward hydrocarbons was given by the catalyst supported on V3G, with large metal particle size which, at the same time, exhibited a lower decrease in activity with reaction time than the other Fe catalysts with smaller average particle size. The olefin/paraffin ratio is very large for the catalyst prepared from Fe(CO)₅.The Ru catalysts are essentially of the methanation type.     

Comparative study of Cu/ZnO catalysts derived from different precursors as a function of aging

Structural modifications of Cu/ZnO catalysts for methanol steam reforming (MSR) as a function of precipitate aging in catalysts preparation process has been investigated comparatively. Freshly precipitated Cu,Zn-hydroxycarbonate (HC) and Cu,Zn-hydroxynitrate (HN) were aged in their mother liquor for a period of 120 min followed by washing, drying, calcination and reduction. Pronounced effect of aging was found for aged HC precipitates while no significant effect of aging was observed for aged HN solids. The bulk structure of the Cu/ZnO catalysts was investigated by means of TG/MS, in situ XRD and ⁶³Cu NMR. The increase in the activity of the catalysts prepared by HC aging did not correlate linearly with the specific Cu surface area but coincides with an increase in the microstrain in the copper clusters presumably because of the improved interface between Cu and ZnO. Meanwhile, aging of HN precipitates results in large, separated and less strained Cu and ZnO particles with an inferior catalytic activity. Finally, both aged Cu/ZnO catalysts revealed smaller copper crystallite size compared to unaged samples.     

Development of cobalt catalysts for the steam reforming of naphthalene as a model compound of tar derived from biomass gasification

The catalytic performances of Co/MgO catalysts for the steam reforming of naphthalene were investigated. The results of characterizations (TPR, XRD, CO adsorption, and CO-TPD) showed that large-sized Co metal particles were formed over the catalysts pre-calcined at 873 K with high Co loading via reduction of Co₃O₄ and MgCo₂O₄ phases. A few Co metal particles were obtained over the catalysts pre-calcined at 1173 K with all Co loading values after reduction.The catalytic performances data showed that 12 wt.% Co/MgO catalyst pre-calcined at 873 K exhibited the best catalytic performance (conv., 23%, 3 h) for the steam reforming of naphthalene among the catalysts tested in this study, due to the existence of Co metal and the low amounts of coke deposition. On the other hand, the data also revealed that the reaction of steam reforming of naphthalene proceeds over all Co-loaded catalyst pre-calcined at 1173 K initially; however, the deposition of the polymer of C_nH_m radicals and the oxidation of catalysts by H₂O led to the decrease of activity.It should be noted that 12 wt.% Co/MgO catalyst pre-calcined at 873 K showed high and stable activity under the low steam/carbon mole ratio (0.6), with H₂ and CO₂ as main products. These two excellent advantages serve to increase the overall biomass gasification system energy efficiency and allow using the product gas for fuel cell system. Thus, Co catalyst is a promising system for the steam reforming of naphthalene derived from biomass gasification as a second fixed catalytic bed.     

Heterogeneous Fenton catalyst derived from hydroxide sludge as an efficient and reusable catalyst for anthraquinone dye degradation

Hydroxide sludge (HS) is the main by-product of drinking water production stations. In our work, we have promoted the valorization of these sludge, we convert it into activated carbon to serve as a support as a heterogeneous Fenton catalyst for reactive blue 19 (RB 19) degradation. The HS and Fe/HS-300 were characterized by means of SEM, EDX-ray, FTIR and XRD analysis. RB 19 and TOC removals were 92% and 41% respectively in optimal condition. More importantly, Fe/HS-300 exhibited an excellent stability and low Fe ion leaching (0.2–0.7mg/L), it was recycled 6 runs still maintaining the same efficiency.     

Fe1-XO基氨合成催化剂的化学特性及其工业应用

Fe_1-XO基催化剂具有特殊维氏体相结构、高铁比、易还原、还原出水少且时间短、低温低压下活性高等特点。为充分发挥Fe_1-XO基催化剂的优异性能，对其工业上的应用进行了分析讨论。     

Novel Fe/MnK‐CNTs nanocomposites as catalysts for direct production of lower olefins from syngas

Novel Fe/MnK‐CNTs nanocomposites are developed as catalysts for direct production of lower olefins from syngas, delivering a high iron time yield of 337.2 μmol_CO· ·s^?1 with 51.3%C selectivity toward C₂?C₄ olefins under the optimal reaction conditions (270°C, 2.0 MPa, 30,000 mL h^?1 ). These catalysts are optimized by varying calcination temperature from 150 to 400°C. Multiple techniques including transmission electron microscopy, Elemental mapping, X‐ray diffraction, X‐ray photoelectron spectroscopy, H₂‐temperature‐programmed reduction, and Raman were employed to reveal the relationship between the catalyst nature and unique catalytic behavior. In particular, the resultant catalyst from the calcination temperature of 220°C exhibits the highest selectivity of C₂?C₄ olefins as well as good stability, which are enabled by the trade‐off among the effects of iron particle sizes, promoters, metal‐support interaction and support surface chemistry. Moreover, influences of reaction temperature, reaction pressure and space velocity are also investigated. © 2016 American Institute of Chemical Engineers AIChE J, 63: 154–161, 2017     

The kinetics of combustion of chars derived from sewage sludge

Experiments have been conducted to determine the combustion characteristics of sewage sludge chars in electrically heated beds of silica sand fluidised by air. The effects of the initial size of the char particles, the temperature of the bed and [O₂] in the fluidising gas were investigated. Also, the temperatures of burning particles were measured with embedded thermocouples. The kinetics of combustion were measured at temperatures low enough for the CO formed by initial reaction between the carbon and oxygen to burn at some distance away from the particle. Accordingly, the particle is only heated by the enthalpy of the reaction C+0.5O₂→CO. The activation energy for the intrinsic kinetics of combustion of the char was estimated to be 130–144 kJ/mol. The former value makes allowance for the fact that the particles are at a temperature in excess of that of the bed (determined by a heat balance on a reacting particle), whilst the latter value assumes that the particles are at the same temperature of the bed. It is probable that the lower value is closer to the actual value, thought to be 135±15 kJ/mol, reflecting the catalytic nature of the ash skeleton on which the carbon is supported. It was possible to obtain good agreement between measured burnout times and those predicted using the grain model of Szekely J, Evans JW, Sohn HY. Gas–solid reactions. New York: Academic Press; 1976, for the case where the kinetics are controlled by a combination of: (i) external mass transfer of oxygen from the particulate phase to the external surface of the burning char particle, (ii) diffusion of oxygen from the external surface into the porous matrix to the surfaces of grains, of which the solid is composed, and (iii) diffusion of oxygen into the microporous grains, where reaction occurs with the carbon. It was found that, for particles with diameters of 2 mm or larger, the initial rates of reaction, for bed temperatures in excess of 750 °C, are dominated by external mass transfer. This explains the dependence of the rate of oxidation of unit mass of char on 1/d_p, and the relatively small influence of temperature on these rates. Particles of char from sewage sludge are so reactive that it is essential to make allowance for a difference in temperature between the particle and the bed. Thus, experimental determinations on particles with d_p∼6.5 mm, suggested a difference in temperature of ∼150 K, in line with calculations using a steady-state heat balance.     

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.     

Oxidized carbon as a support of copper oxide catalysts for methanol decomposition to hydrogen and carbon monoxide

Copper oxide supported on oxidized activated carbon is investigated as a catalyst for methanol decomposition to H₂ and CO. The influence of the medium of the precursor deposition on the state of the active phase is observed. The role of the chemical nature of the support in the formation of catalytic active complex is discussed.     

The search for new solid acid catalysts: systems derived from phosphatoantimonates

A series of potassium phosphatoantimonates (KSbP₂O₈, KSb₂PO₈, K₂SbPO₆ and K₃Sb₃P₂O₁₄) crystallizing in a variety of structures (one-, two- and three- dimensionally extended) has been converted to the protonic form and tested for catalytic efficiency in the dehydration of methanol. The predominant product in all cases is dimethyl ether, and the most active is the layered acid HSbP₂O₈ which reaches its maximum activity at a temperature of about 350 °C.     

制浆造纸厂富铁污泥中Fe3+的电化学还原研究

采用电化学法将制浆造纸厂废水Fe^nton氧化产生的难处理富铁污泥中的Fe^3+还原为Fe^2+,以便于其再利用。研究表明,以不锈钢为阴极材料可较大幅度降低Fe^3+还原的过电位;当Fe^3+质量浓度为2000 mg/L时无需辅助电解质,在极水比为0.48 cm^2/mL,电流密度为0.65 mA/cm^2的条件下反应2 h,Fe^2+再生率可达60.1%,电流效率为92.1%。将酸处理后的富铁污泥溶液在上述条件下还原3 h,Fe^2+再生率达68.8%,电流效率近100%。电化学法是富铁污泥中Fe^3+再利用的可行方法。