Molecular Approach to the Mechanism of Deposition−Precipitation of the Ni(II) Phase on Silica

Abstract

A molecular mechanism explaining the chemical phenomena that occur during the preparation of silicasupported nickel catalysts by the method of deposition-precipitation is proposed. This mechanism takes into account the fact that either 1:1 nickel phyllosilicate or nickel hydroxide may be formed on silica during deposition-precipitation, depending on the silica surface area and the deposition-precipitation time, as shown in our previous paper (Burattin, P.; Che, M.; Louis, C. J. Phys. Chem. B 1997, 101, 7060). The mechanism is mainly based on the kinetic competition between two types of reactions: (i) Ni-O-Si heterocondensation/ polymerization, which leads to the growth of 1:1 nickel phyllosilicate on a Ni(II) brucitic layer bonded to silica; (ii) Ni-OH-Ni olation/polymerization, which leads to the formation and the growth of nickel hydroxide on a Ni(II) brucitic layer bonded to silica. The former type of reaction is faster than the latter but is limited by the concentration in solution of silicic acid arising from silica dissolution and by its diffusion rate. The changes in the pH curves, the yield of Ni(II) deposition-precipitation, and the nature of the supported Ni(II) phase during deposition-precipitation under different experimental conditions are also interpreted on the basis of the mechanism proposed.

Liquid Phase Hydrogenolysis of Biomass‐derived Lactate to 1,2‐Propanediol over Silica Supported Cobalt Nanocatalyst

“…In contrast, amorphous lamellar structure constituted of claylike lines is observed clearly in DP catalyst, suggesting the presence of cobalt phyllosilicate species. [43][44][45] These findings are in good agreement with results obtained by XRD, in situ XRD, XPS and TPR. …”

“…According to Louis et al, 44 the molecular mechanism of Co-OH-Co olation condensation is employed to interpret the chemical phenomenon in the solution and the formation of supported Co(OH) 2 during the precipitation-gel process.…”

“…According to Louis et al 44 Si-O-Co oxolatio heterocondensation and Co-OH-Co olation condensation are competitive reactions occurring in the solution. The characterization result also indicated that the kinetics of Si-O-Co condensation is expected to be faster than that of Co-OH-Co condensation during the deposition-precipitation process.…”

Design, Synthesis, and Mechanistic Evaluation of Iron-Based Catalysis for Synthesis Gas Conversion to Fuels and Chemicals

“…These results indicate that the surfactant removal process and the prevention of the re-oxidation of small metallic Co clusters during this process are essential to form small supported Co metal clusters via colloidal methods. Homogeneous deposition-precipitation (HDP) techniques provide another approach to synthesize high loadings of dispersed metal oxide clusters on supports [45,46]. This method allows the deposition of a soluble metal salt exclusively onto a support surface via gradual and homogeneous introduction of a precipitation agent, for example, hydroxyl ions, to prevent the nucleation of the precursor away from surfaces in the homogeneous phase.…”

Synthesis of Tetrahydropyran from Tetrahydrofurfuryl Alcohol over Cu–Zno/Al2O3 under a Gaseous-Phase Condition

“…Figure 2 shows the H2-TPR profile of the calcined catalysts, and an asymmetrical peak can be observed. Generally, the reduction temperature of copper species changes with particle size, chemical environment, and the metal support interaction of Cu oxide species [40,41]. The intensity of reduction peak was reduced with the increased addition of γ-Al2O3 due to the decrease in Cu content.…”