Structural evolution in Pt/Ga-Zn-oxynitride catalysts for photocatalytic reforming of methanol

Abstract

Products of microwave-assisted urea-induced co-precipitation of Ga(NO 3 ) 3 and Zn(NO 3 ) 2 or Ga 2 O 3 and ZnO were nitridated in order to obtain Ga-Zn-based photocatalysts. Irrespectively to the starting material, wurtzite-like Ga-Zn-oxynitride phases formed. The preparation was completed by deposition of a Pt co-catalyst, which was activated by either reduction in hydrogen or calcination in air. It was demonstrated by X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) that during oxidative activation the oxynitride started to transform into a nitrogen-free Zn-containing Gaoxyhydroxide. Regardless to the structure of the catalysts after the activation step, almost complete oxynitride to oxyhydroxide transformation was observed during the methanol photocatalytic reforming reaction, accompanied by complete reduction of the Pt co-catalyst to metallic state. The observations of this study point to the importance of phase transitions under reaction conditions in the development of the active ensemble in the Ga,Zn-based photocatalysts.

Structural transformation of Ga2O3-based catalysts during photoinduced reforming of methanol

“…Its finding in our experiments suggests that the presence of Pt can induce the phase transition of -Ga 2 O 3 into GaOOH in the aqueous medium under the long time (600 min) irradiation. The appearance of GaOOH is consistent with our previous finding, i.e., Ga-Zn-oxyhydroxide forms as a result of the photoinduced reforming of methanol over Pt loaded Ga-Zn-oxynitride [34].…”

“…Upon using Pt cocatalysts the highest activity was obtained if it was prepared by impregnation followed by calcination in air [21]. In our previous work on using Ga-Zn oxynitrides for methanol photocatalytic reforming, we also found that Pt cocatalyst formation by calcination was more favorable than that by high temperature H 2 treatment [34]. However, the presence of Pt cocatalyst in any form resulted in a transformation of the oxynitride phase into oxyhydroxide during the photoinduced reaction [34].…”

“…The photoinduced reforming reaction was carried out similarly to our previous study [34]. An UV-Consultig Peschl UV-Reactor System 1 equipped with gas inputs and outputs was used as a photoreactor.…”

Graphite Oxide-TiO2 Nanocomposite Type Photocatalyst for Methanol Photocatalytic Reforming Reaction

“…Correlations between the photocatalytic behavior and the interaction of the carbonaceous material and the semiconductor were sought. Our recent results revealed that the working conditions of the methanol photocatalytic reforming reaction may result in significant changes of the structure of certain metal oxide-semiconductor catalyst systems involving both the semiconductor [54] and co-catalyst [15] compared to the fresh state. Therefore we characterized both the fresh and recovered samples by bulk and surface characterization methods such as diffuse reflectance UV-Vis, 13 C MAS NMR, ATR-IR spectroscopy and XPS.…”

Multimetallic Oxynitrides Nanoparticles for a New Generation of Photocatalysts

“…[9] Currently,t he ZnO:GaN solid solutionsa re alwaysp repared by nitridation of the mixed oxide commonly by co-precipitation and more recently by sol-gelb ased processes;h owever, so far alwaysu nder NH 3 flow as nitrification agent. [9,10] Commons tarting materials are the single or mixed oxides, [11,12,13,14] hydroxide, [15] gel-like precursors, [16] Zn/Ga/CO 3 layered double hydroxides [17] or ammonolysis of amorphous precursors. [18] Even when urea was used as nitrogen source, the synthesis required the preparation of hydroxides, which were treated at 900 8Cu nder ammonia flow.…”