Margarita Gabrovska

Water-gas shift reaction over nickel hydroxides

Charcoal-supported nickel hydroxides were investigated in the water-gas shift reaction and found to exhibit high catalytic activity. Nickel hydroxide structures of the type α*-Ni(OH)2·xH2O are supposed to be the most probable bearers of the catalytic activity. A redox Ni2+⇌Ni3+ transition is accomplished in these catalysts.

Effect of the support and the reduction temperature on the formation of metallic nickel phase in Ni/silica gel precursors of vegetable oil hydrogenation catalysts

Ni/SiO2 materials with identical composition (SiO2/Ni = 1.0) have been synthesized by precipitation of Ni(NO3)2 · 6H2O solution with Na2CO3 solution on the silica gel, obtained at three different pH values. The present investigation was undertaken in an endeavor to study the effects of the silica gel support type and the reduction temperature on the formation and dispersion of the metallic nickel phase in the reduced Ni/SiO2 precursors of the vegetable oil hydrogenation catalyst. The physicochemical characterization of the unreduced and reduced precursors has been accomplished appropriately by powder X-ray diffraction, infrared spectroscopy, temperature programmed reduction and H2-chemisorption techniques. It can be stated that the texture peculiarities of the silica gels used as supports influence on the crystalline state and distribution of the deposited Ni-containing phases during the preparation of the precursors, on the reduction temperature of the investigated solids as well as on the bulk size and surface dispersion of the arising metallic nickel particles. It was shown that two types of Ni2+-species are formed during the synthesis procedure, namely basic nickel carbonate-like and Ni-phyllosilicate with different extent of presence, location and strength of interaction. The different location of these species is supposed to result in various strength of Ni-O and Ni-O-Si interaction, thus determining the overall reducibility of the precursors. It was specified that the Ni2+-species are strongly bonded to the surface of the silica gel obtained at neutral pH value and weakly bonded to the surface of those prepared in acidic and alkaline conditions. It was established that the precursor, derivates from the silica gel obtained at alkaline conditions, demonstrates both significant reduction of the Ni2+ ions at 430°C and finely dispersed metallic nickel particles on its surface. High dispersion of the metallic nickel might be the crucial reason for achieving of high activity in the vegetable oil hydrogenation.

Catalytic performance of Ni-Al layered double hydroxides in CO purification processes

Ni-Al layered double hydroxides with Ni2+/Al3+ molar ratios of 1.5 and 3.0 have been synthesized by co-precipitation and studied as catalyst precursors for purification of CO-containing gas-mixtures by means of CO oxidation to CO2 and conversion of CO by water vapor (water-gas shift reaction). The influence of the alkali additives (K+ ions) on the water-gas shift activity has been also examined. It was established that the catalytic activity of both reactions increases with the temperature and the nickel content. Hypothetic schemes are proposed about activation of the catalysts in the WGSR and CO oxidation including redox Ni2+ ↔ Ni3+ transition on the catalyst surface. The activity in WGSR is positively affected by the presence of potassium promoter, depending on its amount. The sample with higher nickel loading is the most effective catalyst as for CO oxidation as well as for WGSR at intermediate temperatures after potassium promotion.

The state of nickel in the silver modified NiMg/SiO2 vegetable oil hydrogenation catalysts

Two series of silver modified Ni-Mg materials were synthesized by precipitation-deposition on SiO2 support derived from two silica sources: diatomite activated at 800°C (Series a; Mg/Ni = 0.1 and SiO2/Ni = 1.07) and synthetic water glass (Series b; Mg/Ni = 0.1 and SiO2/Ni = 1.15). The modification with silver was made at three molar Ag/Ni ratios, namely 0.0025, 0.025, and 0.1. The effects of the source of the silica support and the silver presence and content on the nickel state in the silver modified reduced-passivated NiMg/SiO2 precursors of the vegetable oil hydrogenation catalyst were established by X-ray diffraction and X-ray photoelectron spectroscopy techniques. The passivation procedure was applied in order to protect the metallic nickel particles from further oxidation. The crystallization of the formed nickel hydrosilicate phases depends on the source of the silica support, more expressed in the diatomite supported samples. It was shown that the silver modification of the NiMg/SiO2 precursors enhances the reduction of the nickel hydrosilicates accompanied by formation of relatively smaller metallic nickel particles, more pronounced in the water glass supported precursors. The increase of the silver content in the water glass deposited samples is responsible for the metallic nickel dispersion increase. The higher content of the Ni0 particles on the surface of the diatomite deposited samples is in accordance with the higher stability of the larger metallic nickel crystallites to oxidation during the passivation step. On contrary, higher dispersed Ni0 particles on the surface of the water glass supported samples are more susceptible to the oxida

Supported Nickel-Based Catalysts for Partial Hydrogenation of Edible Oils

Nickel-based catalysts, supported on diatomite, silica gel and perlite, with high nickel loadings, have been prepared by precipitation-deposition method. Various nickel precursor salts were used for the preparation of catalyst precursors. In the precursor state, the catalysts were characterized using nitrogen physisorption, mercury porosimetry, infrared, and X-ray diffraction spectroscopy. The reducibility of catalyst precursors was evaluated using hydrogen temperature programmed reduction. Hydrogen chemisorption and X-ray photoelectron spectroscopy measurements were performed with the aim of characterizing the chemical state of the catalyst precursors. This research was focused on the study of some major factors on the state, dispersion and reducibility of a deposited Ni phase by the combined use of mentioned experimental techniques. We have examined the influence of the nature of support and the use of modifiers on activity of nickel-based catalysts in the partial hydrogenation of sunflower and soybean oils. Nitrogen physisorption and mercury porosimetry data showed that synthesis operating conditions and pore structure of supports have a profound effect on the textural properties of catalyst precursors. The analysis of infrared and X-ray diffraction spectra showed the existence of chemical species and phases which indicate the different extent of interaction between the support and the active metal. Temperature programmed reduction study revealed that the reduction features depend on the identity of the nickel precursor salt and its interaction with the support. A stronger interaction of the supported Ni phase with support hinders the reduction of catalyst precursors. Hydrogen chemisorption results showed the presence of nickel crystallites varying from 5 to 47 nm in size. The X-ray photoelectron spectroscopy data confirmed the formation surface species with different strength of interaction and different nickel crystallite sizes. The hydrogenation results showed significant differences, depending on the support and the modifier, as well as structural characteristics of reduced catalyst precursors. The results show the importance of modifiers in the control of the activity and selectivity of the partial hydrogenation

Perlite as a potential support for nickel catalyst in the process of sunflower oil hydrogenation

Investigation was conducted in order to elucidate the possibility of using perlite as support for preparation of nickel based precursor catalyst, potentially applicable in vegetable oil hydrogenation process. On three differently prepared expanded perlite, nickel catalyst precursors with identical Ni/SiO2 = 1.1 and Ni/Mg = 10/1 ratios were synthesized by precipitation-deposition method. Different techniques, SEM micrography, He-pycnometry, calcimetry, Hg-porosimetry, N2-physisorption, H2-chemisorption and temperature programmed reduction, were used for characterization of obtained samples. Determining the precursor texture, morphology and reducibility shows a successfully deposited nickel phase on perlite support with promising properties for vegetable oil hydrogenation. Chosen precursor was reduced and passivated in paraffin oil and the obtained catalyst showed significant catalytic activity in the test of sunflower oil hydrogenation.

Ni–Al Layered Double Hydroxides as Precursors of Ceramic Pigments

Ni–Al layered double hydroxides with a ratio of Ni2+/Al3+ = 0.5, 1.5, and 3.0 were prepared by co-precipitation followed by stepwise heating in the range 473–1273 K in an air. The solids were investigated using specific surface area measurements, powder X-ray diffraction, scanning electron microscopy, infrared spectroscopy, diffuse reflectance spectroscopy, and magnetic susceptibility. It was found that the color of the obtained oxide derivatives, varying from pale green to dark turquoise, cyan, or pale blue, is determined by the coordination state of the Ni2+ ions depending on the nickel content and the calcination temperature of the Ni–Al layered precursors. Owing to its chemical composition, homogeneity and morphological characteristics, the nanosized well-defined single-phase NiAl2O4 spinel is suitable candidate for obtaining fine-colored cyan or pale blue nano-pigments. The proposed pigments represent less expensive alternative to blue CoAl2O4 spinel for some glaze applications. Finally, Ni–Al layered double hydroxides represent appropriate materials for the preparation of ceramic pigments with different properties and applications.