S. A. Khromova

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.

Effect of the Ni/Cu ratio on the composition and catalytic properties of nickel-copper alloy in anisole hydrodeoxygenation

The activity of NiCu-SiO2 catalysts with a metal content of 90% and different Ni/Cu ratios has been investigated in the hydrodeoxygenation of anisole, a model compound of bio-oil, at 280°C and 6 MPa. A homogeneous phase composition of the active component has been synthesized by the co-decomposition of nickel and copper nitrates followed by the introduction of SiO2 as a stabilizer. The resulting catalysts have been characterized by temperature-programmed reduction, X-ray powder diffraction, X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy combined with energy-dispersive microanalysis. The bulk and surface composition of active-component particles has been determined by XPS and X-ray diffraction. In all of the catalysts containing 15–85 wt % Ni, there are two types of solid solutions. One has a constant composition, Cu0.95Ni0.05, which is independent of the Ni/Cu ratio in the catalyst; in the other, the nickel stoichiometry increases with an increasing Ni content of the active component. A correlation has been established between the Ni/Cu ratio and the rate constants of the reaction examined and between the Ni/Cu ratio and the degree of hydrodeoxygenation for all samples. The most active catalyst is Ni85Cu5-SiO2.

Stability of nickel-containing catalysts for hydrodeoxygenation of biomass pyrolysis products

Heterogeneous catalysts for the hydrotreatment (hydrodeoxygenation) of biomass fast pyrolysis products (bio-oil) for the production of fuel hydrocarbons are considered. Hydrodeoxygenation catalysts are conventionally divided into three groups: catalysts based on noble metals, sulfided catalysts for desulfurization, and non-sulfided catalysts based on supported transition metals. The main emphasis in this work is on nickel-based non-sulfided catalytic systems as the ones most promising for the hydrotreatment of feedstocks with low content of sulfur. In light of specific features of bio-oil (high acidity and viscosity, low thermal stability), requirements are formulated that must be met in developing hydrodeoxygenation catalysts and processes based on them, especially specifications for the stability of catalysts of this type and their ability for multiple regeneration.

Catalytic hydrotreatment of fast pyrolysis liquids in batch and continuous set-ups using a bimetallic Ni–Cu catalyst with a high metal content

In this paper, an experimental study on the hydrotreatment of fast pyrolysis liquids is reported in both batch and continuous set-ups using a novel bimetallic Ni–Cu based catalyst with high Ni loading (up to 50%) prepared by a sol–gel method. The experiments were carried out in a wide temperature range (80–410 °C) and at a hydrogen pressure between 100–200 bar to determine product properties and catalyst performance as a function of process conditions. To gain insight into the molecular transformations, the product oils were analysed by GC × GC, 1H-NMR and GPC and reveal that the sugar fraction is reactive in the low temperature range ( 300 °C). In addition, the organic acids are very persistent and reactivity was only observed above 350 °C. The results are rationalized using a reaction network involving competitive hydrogenation of reactive aldehydes and ketones of the sugar fraction of fast pyrolysis liquids and thermal polymerisation. In addition, relevant macro-properties of the product oils including flash point (30 to 80 °C), viscosity (0.06 to 0.93 Pa s) and TG residue (<1 to about 8 wt%) were determined and compared. Product oils with the lowest oxygen content (<13 wt%) were obtained in the continuous set-up at 410 °C.

In situ powder X-ray diffraction study of the process of NiMoO4–SiO2 reduction with hydrogen

An interest in NiMoО4–SiO2 reduction stems from its promising use as catalysts for hydrodeoxygenation and hydrodesulfurization processes. The work exploits in situ X-ray diffraction to investigate phase transformations during NiMoO4–SiO2 reduction with hydrogen in a temperature range of 30-700°C. The α-NiMoО4 reduction is shown to proceed in two stages. In the first stage, at 400-500°C, an intermediate state (Ni,Mo,□)O mixed oxide and Ni1–xMox form. In the second stage, above 650°C, two solid solutions based on the Mo and Ni structures form. The structure of the intermediate state is refined by the Rietveld method. It is demonstrated that the Ni–Mo mixed oxide forms based on the NiO structure, which contains a certain number of cation vacancies.