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Zirconium-loaded mesostructured silica nanoparticles (Zr/MSN) were developed for the removal of hexavalent chromium (Cr(VI)) from aqueous solutions. X-ray diffraction, transmission electron microscopy, and Brunauer− Emmett−Teller results revealed that both MSN and Zr/MSN showed a characteristic highly ordered hexagonal pore structure with a high specific area of 821−1219 m 2 g −1 . Fourier transform infrared analysis showed that the presence of Zr diminished the absorbance band that was assigned to silanol groups of the structural defect sites, while XPS analysis of the binding energy of Si−O−Zr indicated interactions between the silanol groups and zirconium. The interaction of zirconium and silanol groups from the structural defect sites generated bidentate zirconium, which acted as an active site for the adsorption. The experimental results showed that the modification of MSN with zirconium significantly enhanced the adsorption capacity for Cr(VI). The equilibrium isotherm data showed that the adsorption process was best described by the Langmuir isotherm with 104 mg g −1 maximum adsorption capacity, while the kinetics of Cr(VI) adsorption followed a pseudo-second-order kinetic model. The thermodynamic properties confirmed that the adsorption of Cr(VI) onto Zr/MSN was spontaneous and endothermic in nature, with an activation energy of 24 kJ mol −1 showing that the adsorption was a chemisorption process.

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Nickel (Ni), cobalt (Co), and zinc (Zn) loaded on fibrous silica KCC-1 was investigated for CO methanation reactions. Ni/KCC-1 exhibits the highest catalyst performance with a CH formation rate of 33.02 × 10 mol mol s, 1.77 times higher than that of Co/KCC-1 followed by Zn/KCC-1 and finally the parent KCC-1. A pyrrole adsorption FTIR study reveals shifting of perturbed N-H stretching decreasing slightly with the addition of metal oxide, suggesting that the basic sites of catalyst were inaccessible due to metal oxide deposition. The strengths of basicity were found to follow sthe equence KCC-1, Ni/KCC-1, Zn/KCC-1, and Co/KCC-1. The data were supported by N adsorption desorption analysis, where Co/KCC-1 displayed the greatest reduction in total surface area whereas Ni/KCC-1 displayed the least reduction. The elucidation of difference mechanism pathways has also been studied by in situ IR spectroscopy studies to determine the role of different metal oxides in CO methanation. It was discovered that Ni/KCC-1 and Co/KCC-1 follow a dissociative mechanism of CO methanation in which the CO molecule was dissociated on the surface of the metal oxide before migration onto the catalyst surface. This was confirmed by the evolution of a peak corresponding to carbonyl species (CO) on a metal oxide surface in FTIR spectra. Zn/KCC-1, on the other hand, showed no such peak, indicating associative methanation pathways where a hydrogen molecule interacts with an O atom in CO to form CO and OH. These results offers a better understanding for catalytic studies, particularly in the field of CO recycling.

Dendrimeric fibrous silica HZSM-5 (HFSZ) catalysts were prepared using a microemulsion technique and ZSM-5-seeding crystallization with different oil phases, benzene, toluene, and xylene, and denoted as FB, FT, and FX, respectively. The HFSZ catalysts possessed a well ordered crystalline structure with chestnut-like spherical particles, rich with dendrimeric fiber morphology. It was found that the hydrophobicity of the oil phase significantly affected the physicochemical properties of the HFSZ catalysts that altered their activity toward benzene methylation. The density of dendrimeric fibers and ensuing acidities were found to play crucial roles in enhancing the selective production of toluene and p-xylene via transalkylation and dealkylation of bulkier aromatics. The production of ethylbenzene (EB) using commercial HZSM-5 could be suppressed to give major products of toluene (84%) and p-xylene (58%) when using FB and FX at 673 and 623 K, respectively.