Influence of organic additives on the properties of impregnation solutions and on nickel oxide particle size for Ni/Al2O3 catalysts

The Effects of Ce and W Promoters on the Performance of Alumina-Supported Nickel Catalysts in CO2 Methanation Reaction

The influence of Ce and W promoters on the performance of alumina-supported nickel catalysts in the CO2 methanation reaction was investigated. The catalysts were obtained by the co-impregnation method. Nitrogen low-temperature adsorption, temperature-programmed reduction, hydrogen desorption, transmission electron microscopy, X-ray diffraction, and photoelectron spectroscopy studies were used for catalyst characterization. An introduction of Ce and W promoters (1–5 wt %) led to the decrease in mean Ni crystallite size. Gradual increase in the active surface area was observed only for Ce-promoted catalysts. The increase in CO2 conversion in methanation reaction at low-reaction temperatures carried out over Ce-promoted catalysts was attributed to the increase in the active surface area and changes in the redox properties. The introduction of small amounts of tungsten led to an increase in the activity of catalysts, although a decrease in the active surface area was observed. Quasi in situ XPS studies revealed changes in the oxidation state of tungsten under CO2 methanation reaction conditions, indicating the participation of redox promoter changes in the course of surface reactions, leading to an improvement in the activity of the catalyst.

Oxy-Steam Reforming of Natural Gas on Ni Catalysts—A Minireview

Nowadays, the reforming of natural gas is the most common of hydrogen or syngas generation process. Each reforming process leads to the achievement of specific goals and benefits related to investment costs. The disadvantage of the reforming process is the need to preclean it mostly from the sulfur and nitrogen compounds. The solution to this problem may be liquefied natural gas (LNG). Liquefied natural gas has recently been seen as an energy source and may be a promising replacement for natural gas. The constant development of the pipeline network, safe transport and a lot of advantages of LNG were contributed to the research development related to the usage of LNG in energy generation technologies. The presented review is a literature discussion on the processing of methane used to produce hydrogen with particular emphasis on the processes of oxy-steam reforming of natural or liquefied natural gas (OSR-LNG). In addition, a key consideration in this article includes Ni catalyst systems used in the oxy-steam reforming of methane or LNG reactions. An analysis of the OSR process conditions, the type of catalyst and the OSR of the methane reaction mechanism may contribute to the development of a modern, cheap catalyst system, which is characterized by high activity and stability in the oxy-steam reforming of natural gas or LNG (OSR-LNG).

Application of POSS Nanotechnology for Preparation of Efficient Ni Catalysts for Hydrogen Production

POSS (polyhedral oligomeric silsesquioxanes) nanotechnology was applied for preparation of efficient Ni catalysts for hydrogen production through autothermal reforming of methane (ATR of CH4). The novel metal-POSS precursor [Nickel (II) ‒ HeptaisobutylPOSS (C4H9)7Si7O9(OH)O2Ni] of Ni nanoparticles was introduced into Ce0.5Zr0.5O2 support with following calcination and reduction stages of activation. The peculiarity of the genesis of Ni/SiO2/Ce0.5Zr0.5O2nanomaterials and their characteristics versus deposition mode were studied by X-ray fluorescence spectroscopy, thermal analysis, N2adsorption, X-ray diffraction, high-resolution transmission electron microscopy and H2 temperature-programmed reduction. The two kinds of supported Ni-containing particles were observed: highly dispersed Ni forms (1‒2 nm) and large Ni-containing particles (up to 50‒100 nm in size). It was demonstrated that the textural, structural, red-ox and, consequently, catalytic properties of ex-Ni-POSS catalysts depend on the deposition mode. The increase of a portion of difficultly reduced Ni2+species is found upon application of intermediate calcination during Ni-POSS deposition that has detrimental effect on the activity of catalyst in ATR of CH4. The Ni/SiO2/Ce0.5Zr0.5O2 catalyst prepared by one-step Ni-POSS deposition exhibits the highest H2 yield ‒ 80% at T = 800 °C.

Molecularly Tailored Nickel Precursor and Support Yield a Stable Methane Dry Reforming Catalyst with Superior Metal Utilization

Syngas production via the dry reforming of methane (DRM) is a highly endothermic process conducted under harsh conditions; hence, the main difficulty resides in generating stable catalysts. This can, in principle, be achieved by reducing coke formation, sintering, and loss of metal through diffusion in the support. [{Ni(μ²-OCHO)(OCHO)(tmeda)}₂(μ²-OH₂)] (tmeda = tetramethylethylenediamine), readily synthesized and soluble in a broad range of solvents, was developed as a molecular precursor to form 2 nm Ni(0) nanoparticles on alumina, the commonly used support in DRM. While such small nanoparticles prevent coke deposition and increase the initial activity, operando X-ray Absorption Near-Edge Structure (XANES) spectroscopy confirms that deactivation largely occurs through the migration of Ni into the support. However, we show that Ni loss into the support can be mitigated through the Mg-doping of alumina, thereby increasing significantly the stability for DRM. The superior performance of our catalytic system is a direct consequence of the molecular design of the metal precursor and the support, resulting in a maximization of the amount of accessible metallic nickel in the form of small nanoparticles while preventing coke deposition.

Impact of double-solvent impregnation on the Ni dispersion of Ni/SBA-15 catalysts and catalytic performance for the syngas methanation reaction

Ni/SBA-15 prepared by a double-solvent impregnation method showed excellent activity for CO methanation and catalyst sintering was the main cause of deactivation.