Structuring-agent role in physical and chemical properties of Mo/SiO2 catalysts by sol-gel method
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Molybdenum supported on silica was prepared by the sol-gel method by hydrolysis of tetraethylortosilicate (TEOS) using oxalic acid (OA) or citric acid (CA) as a template through a chelating effect. The effect of the type of template and the molybdenum loading on the structural properties was studied. The relationship between the structure of materials and physical and chemical properties was identified by XRD, FTIR, Raman spectroscopy, H2-TPR, SEM-EDX, and N2 adsorption/desorption techniques. The XRD patterns illustrate that materials prepared varying the type of template and molybdenum loading are in different MoOx species. TPR-H2 analysis shows three different regions attributed to the process of reducing the molybdenum oxide (VI) to molybdenum metal. N2 adsorption/desorption studies reveal the influence of the metal loading and the type of template in the surface area and pore diameter obtained in all the cases values greater when oxalic acid was used. SEM-EDX studies show the similar morphological structures related to silica materials. Finally, the oxalic acid carbonyl groups are less separated which orientates the structure of the silicon oxide towards smaller pores and therefore, larger surface-specific areas with respect to citric acid.
Molybdenum supported on silica was prepared by the sol-gel method modifying the type of template.
Amorphous silica structures were obtained and MoO3 species were observed when the molybdenum load was 6 wt%.
The increase of molybdenum loading produces a decrease in the surface area by the formation of Mo–O–Si or Mo=O–Si bonds.
Oxalic acid allows obtaining materials with higher surface area relative to citric acid.
The larger size of the molecule of citric acid plays an important role as a chelating agent of molybdenum.
KeywordsTemplate role Silica-based materials Molybdenum species Physical and chemical properties
This research was accomplished with financial support from Universidad Nacional de Colombia under 37174 and 40814 projects.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
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