Photocatalytic Production of Vanillin over CeO_x and ZrO₂ Modified Biomass-Templated Titania

Abstract

Walnut shell residues have been used as a sacrificial template in the synthesis of TiO 2 -based materials via mechanochemical synthesis. To improve the photocatalytic efficiency of the synthesized titania nanomaterials, functionalization with ceria and zircona was also investigated. Samples were characterized using a multitechnique approach, including X-ray diffraction, X-ray photoelectron spectroscopy, UV−visible spectroscopy, and scanning electron microscopy. Synthesized materials were employed as catalysts in the photooxidation reaction of vanillyl alcohol toward vanillin, a compound of great interest due to its organoleptic properties. Such photocatalytic experiments were carried out in a batch-type photoreactor using a LED 12 V efficient emission lamp with a wavelength of 395 nm. The use of walnut shell could facilitate the preparation of nanostructured materials. The incorporation of Ce and Zr oxides on the titania surface gave rise to an increased absorption of visible light, together with the improvement of electronic properties, therefore enhancing photocatalytic efficiency as compared to pure TiO 2 . An optimum catalytic behavior was observed for 1Ce/TiO 2 -BS and 5Zr/ TiO 2 -BS, with a maximum conversion of 39.7% and 52.4% for ceria and zirconia modified samples, respectively. Selectivity values of 99% toward vanillin and a carbon balance higher than 98% were achieved in all cases.

Aerobic oxidation of vanillyl alcohol to vanillin catalyzed by air-stable and recyclable copper complex and TEMPO under base-free conditions

“…Various other metal nanoparticles immobilized on a variety of carriers such as metal organic frameworks (MOFs), carbon, titania, and ceria have been also investigated. [59][60][61][62] Photocatalytic oxidations of vanillyl alcohol to vanillin over Ce and Zr oxide supported on biomass-templated titania were also reported by Muñoz-Batista and Luque et al 63 These smart materials showed excellent selectivity (99%) toward vanillin; however, the conversion of vanillyl alcohol was not great (maximum 52%). Similar photocatalytic conversion of vanillyl alcohol to vanillin under mild reaction conditions are reported by other groups.…”

“…Similarly, excellent selectivity could not be achieved using metal nanoparticles. [58][59][60][61][62] Although high selectivity could be achieved using photocatalysts, [63][64][65] poor conversion was a major issue in contrast to complete conversion achieved with the present catalyst. Hence, we can conclude that we have developed a significantly improved catalytic protocols as compared to the existing catalytic system for the aerobic oxidation of vanillyl alcohol to vanillin.…”

Mechanochemical Synthesis of Nickel-Modified Metal–Organic Frameworks for Reduction Reactions

“…182.4 eV, while the distance between Zr 3d 5/2 y Zr 3d 3/2 bands were shown to be ca. 2.5 eV, indicating the formation of Zr (IV) species [30]. Additionally, Ni XPS region was acquired for the three Ni modified samples.…”

Rose-like Bi2WO6 Nanostructure for Visible-Light-Assisted Oxidation of Lignocellulose-Derived 5-Hydroxymethylfurfural and Vanillyl Alcohol

“…Several semiconductor heterojunction photocatalysts have been fabricated to achieve an excellent activity in catalysis and dye degradation, − but only a few photocatalysts have been documented for the photocatalytic conversion of VOL to VAL, which are associated with low VOL conversion and selectivity of VAL. Various heterogeneous photocatalytic materials based on TiO 2 , NiFe 2 O 4 , ZnFe 2 O 4 , CeO 2 , and ZrO 2 and catalysts involving noble metals have been reported for VOL to VAL transformation, − but there is still a need for methods associated with effective oxidation of HMF and VOL, with high product selectivity under mild photocatalytic reaction conditions, using a simple photocatalyst.…”