D.Yu. Ermakov

Effective catalysts for direct cracking of methane to produce hydrogen and filamentous carbon: Part I. Nickel catalysts

Abstract Data obtained by studying model catalytic systems were used to develop high-loaded nickel catalysts for direct cracking of methane into hydrogen and catalytic filamentous carbon (CFC). The approach to the synthesis of these catalysts can be the basis for development of catalytic nickel systems for commercial processing of natural gas. The catalysts were synthesized by fusing nickel nitrate with zirconium nitrate, or nickel nitrate with copper-doped aluminium nitrate followed by decomposition of the mixture at 300–450°C and its additional stabilization by silica. The silica textural promoter was formed by thermal decomposition of polyethoxysilane introduced into pores of the oxide matrix. The catalysts reduced by hydrogen comprised nickel in the amount of 85–90%. Unlike preparation of co-precipitated systems, synthesis of the catalysts mentioned does not include stages of filtration and wastewater treatment. Principal characteristic of the catalysts’ effectiveness for the reaction of decomposition of methane, i.e. carbon yield per gram of nickel, of the suggested systems was close or superior to that achieved before using the best nickel or nickel–copper catalysts prepared by co-precipitation.

Guaiacol hydrodeoxygenation in the presence of Ni-containing catalysts

A series of Ni-containing catalysts supported on different materials has been tested in the hydrodeoxygenation of guaiacol, a compound modeling the products of biomass fast pyrolysis. The reaction has been carried out in an autoclave at 320°C and a hydrogen pressure of 17 MPa. The main guaiacol hydrodeoxygenation products are cyclohexane, 1-methylcyclohexane-1,2-diol, and cyclohexanone (which result from aromatic ring reduction). A guaiacol conversion scheme explaining the formation of the main products is suggested. The highest activity is shown by the Ni-containing catalysts on SiO2 and SiO2-ZrO2 supports prepared by the sol-gel method. According to X-ray diffraction and electron microscopic data, the high activity of these catalysts is due to the high concentration of dispersed nickel as reduced films on the surface of the silicate structures. The catalysts offer promise for refining the biomass fast pyrolysis products (bio-oil) into hydrocarbon fuel.

Nickel catalysts for the hydrodeoxygenation of biodiesel

A number of nickel and nickel-copper catalysts for the hydrodeoxygenation of fatty acid esters (biodiesel) were studied. The CeO2 and ZrO2 oxides and the CeO2-ZrO2 binary system were used as supports. The Ni-Cu/CeO2-ZrO2 catalyst exhibited the highest activity; it allowed us to quantitatively convert biodiesel into linear alkanes under mild conditions (290–320°C, 1.0 MPa). It was found that the selectivity of the formation of the main product (heptadecane) was 70–80%. The main correlations between the nature of catalysts and their activity under conditions of the target reaction were determined using temperature-programmed reduction, X-ray diffraction analysis, and electron microscopy. It was hypothesized that the high activity of Ni-Cu/CeO2-ZrO2 in the test reaction can be explained by the presence of a Ni1 − xCux (x = 0.2–0.3) solid solution as a constituent of the active component of the catalyst.

Chemical properties of the surface of nanofibrous carbonaceous materials produced by catalytic methane decomposition

The chemical behavior of nanofibrous carbonaceous materials prepared by the catalytic decomposition of methane was studied by IR spectroscopy, X-ray photoelectron spectroscopy, and titration. Initial carbon was shown to be virtually devoid of functional groups on its surface. Treatment of carbonaceous samples with alkali, ammonia, or nitric acid modified the surface of carbon and increased the number of functional groups.

Hydrogen production based on the selective catalytic pyrolysis of propane

Catalytic decomposition of propane with producing hydrogen in a temperature range of 400–700°C is investigated. Optimal production parameters (temperature, catalyst composition), which provide the production of a mixture of hydrogen and propane with a low methane content free of carbon oxides for a long time, are established.

Morphology and Texture of Silica Prepared by Sol–Gel Synthesis on the Surface of Fibrous Carbon Materials

Silica materials are synthesized by the sol–gel method including the deposition of tetraethoxysilane on various micro- and nanocarbon fibers. The use of nanofibrous carbon as a template makes it possible to prepare thermally stable mesoporous SiO2 samples with unusually high surface areas (up to 1255 m2/g) and high porosity (up to 5.6 cm3/g). These silica materials and aerogels prepared by supercritical drying have comparable pore volumes. It is found by high-resolution electron microscopy that a thin-wall matrix permeated by channels is a prevailing structure of silica materials. When some catalytic fibrous carbons are used as templates, silica nanotubes can be prepared.

Effect of Interactions between Components in Nickel–Silica Catalysts on the Yield of Carbon in Methane Decomposition

A number of 90% Ni–10% SiO2 catalysts for methane decomposition were studied at different stages of preparation and operation in the reaction using X-ray diffraction analysis, differential dissolution, temperature-programmed reduction, IR spectroscopy, and high-resolution electron microscopy. It was found that an increase in the interaction between components in the catalytic system decreased the ability of nickel to accumulate carbon in the decomposition of methane.