Research Outputs
Evidence of synergy effects between zinc and copper oxides with acidic sites on natural zeolite during photocatalytic oxidation of ethylene using operando DRIFTS studies
In this article, the role of surface sites of modified zeolites with semiconductor nanoparticles as alternative photocatalyts for protecting post-harvest foodstuff from the detrimental effects of ethylene is addressed. Two single and one double catalyst based on zinc and copper oxides supported over modified zeolite samples were prepared. Physical, chemical, and surface properties of prepared materials were studied by several characterization methods. UV-Vis absorption spectra show that the applied modification procedures increase the optical absorption of light in the UV and visible regions, suggesting that an increase in the photocatalytic activity could take place mainly in the obtained co-impregnated catalyst. An ethylene conversion around 50% was achieved when the parent natural zeolite support was modified with both transition metal oxides, obtaining higher removal efficiency in comparison to single oxide catalysts. Adsorption and photocatalytic oxidation experiments were also performed using single and double catalysts supported over fumed silica, attaining lower ethylene conversion and thus highlighting the role of zeolite surfaces as adsorption sites for ethylene during photocatalytic reactions. Operando diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) studies reveal that a synergistic mechanism occurs, involving ethylene adsorption at acidic sites of zeolite and its photocatalytic oxidation due to the generation of radicals by the light activation of nanoparticles of zinc and copper oxides.
New insight of the influence of acidic surface sites of zeolite on the ability to remove gaseous ozone using operando DRIFTS studies
Recently, natural zeolites have started to be used as alternative materials for ozone abatement from working environments. In this study, a surface response methodology based on a D-Optimal design is applied to develop a transition-metal-modified natural zeolite that increases ozone removal efficiency. Ozone adsorption and/or decomposition onto natural and cobalt modified natural zeolite were studied by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Results evidenced that ozone is adsorbed and decomposed at strong Lewis acidic sites, whereas ozone adsorption products interact with surface OH groups. Additionally, DRIFTS studies indicate that nitrous species are adsorbed at acidic sites, reducing the capacity to decompose ozone when ozone is generated from air.
Removal of chlorinated volatile organic compounds onto natural and Cu-modified zeolite: The role of chemical surface characteristics in the adsorption mechanism
In this study, the effect of chemical surface characteristics of natural and Cu-modified zeolite in the adsorption of chlorinated volatile organic compounds (VOCCls) was investigated using infrared spectroscopy. A natural zeolite mainly composed of clinoptilolite and mordenite was used as a parent material. A succession of chemical and thermal treatments produced a Cu-modified natural zeolite (NZ-Cu) with higher adsorption properties toward the elimination of VOCCls. The adsorption of VOCCls onto NZ-Cu zeolite could be explained by a surface mechanism that comprises the interaction not only with Brønsted acid sites present on the original natural zeolite framework; but also with new Brønsted acid sites formed after the successive treatments.