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

TLDR: In this paper, it was demonstrated by X-ray diffraction (XRD), transmission electron microscopy (TEM) and Xray photoelectron spectroscopy (XPS) that during oxidative activation the oxynitride started to transform into a nitrogen-free Zn-containing Ga- oxyhydroxide.

About: This article is published in Materials Research Bulletin.The article was published on 2016-11-01 and is currently open access. It has received 9 citations till now. The article focuses on the topics: Catalysis & Calcination.

Figures

Figure 2. TEM images of the Ga-Zn-oxynitrides obtained by nitridation of different precursors (Zn/Ganom=0.32). A: nitridation of the precipitate from Zn- and Ga- nitrate solution; B: nitridation of oxide mixture; C: commercial GaN. Electron diffraction patterns (inserts) reveal the presence of hexagonal wurtzite (# 76-0703).

Figure 10. Pt 4f spectra of a calcined and a used Pt/Ga-Zn-oxynitride sample obtained from nitridation of the oxide mixture. Zn/Ganom=0.14; Pt content= 1 w%.

Table 4. Characteristic binding energies and element ratios obtained from XPS measurements on the spent Pt-loaded GaN-ZnO photocatalysts Sample/co-catalyst formation Zn/Ganom Ga 3d (eV) Ga AP a (eV) N 1s (eV) N/Ga ratio O 1s (eV) Zn 2p Zn/Ga ratio Pt 4f Ga2O3, Pt calcined -- 20.2 1082.7 -- -- 531.1

Figure 11. Influence of the Pt co-catalyst formation method on the initial period of the hydrogen production reaction. The Ga-Zn-oxyinitride was obtained from oxide mixture; Zn/Ganom=0.14. Lines are only guides to the eye.

Figure 7. XRD pattern of recovered catalysts after the photocatalytic H2 production (reaction conditions in Figure 5) a=sample obtained from precipitate, co-catalyst formation by calcination; b= sample obtained from precipitate, co-catalyst formation by hydrogenation, c= sample obtained from precipitate, co-catalyst formation by hydrogenation, blank experiment, d= sample obtained from oxides, co-catalyst formation by calcination; e= sample obtained from oxides, cocatalyst formation by hydrogenation; f= GaN (commercial), co-catalyst formation by calcination, blank experiment.

Figure 8. TEM images of the Pt/Ga-Zn-oxynitride photocatalysts recovered after the photocatalytic H2 production (reaction conditions in Figure 5). A: used catalyst from precipitate, Pt co-catalyst formed by hydrogenation at 450oC; B: used catalyst from oxide mixture, Pt co-catalyst formed by hydrogenation at 450oC; C: used catalyst from precipitate, Pt co-catalyst formed by calcination at 300oC; D: used catalyst from oxide, Pt co-catalyst formed by calcination at 300oC. Consistently with XRD result, arrows in electron diffraction patterns (inserts) point to GaOOH diffractions (# 87-1901). 101 and 110 indices in C indicate hexagonal wurtzite (# 76-0703) contributions.

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In this paper, the structural evolution in Pt/Ga-Zn-oxynitrides catalysts for photocatalytic reforming of methanol was studied.