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Journal ArticleDOI

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

TL;DR: 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.

Summary (1 min read)

Introduction

  • Photocatalytic hydrogen production is a promising approach for storing solar energy in chemical form.
  • The Ga-Zn-oxynitride ((Ga1-xZnx)(N,O)) structure can be related to the GaN-ZnO solid solution structure by incorporation of more O to the N sites and compensating vacancies to the cationic sites, resulting in an imperfect wurtzite-type material.
  • This co-catalysts/semiconductor system is less effective in the methanol photocatalytic reforming reaction [31].
  • Double distilled water (18 MΩ) was used in every experiments.
  • Energy Dispersive X-ray Spectrometry (EDX) analysis was performed by an INCA (Oxford Instruments Ltd.) detector and an INCA Energy software package attached to a ZEISS EVO 40XVP Scanning Electron Microscope (accelerating voltage: 20kV, Wfilament, working distance 10 mm).

3. Results and discussion

  • All of the samples recovered after high temperature nitridation, obtained either from the precipitates or from the oxide mixtures, had a color of dark yellow to orange.
  • The Zn retention during the nitridation was larger in the samples obtained from precipitates than those from oxides (cf. Zn/Ganom and Zn/GaEDX values in Table 2).

4. Conclusion

  • Ga-Zn-based photocatalysts were prepared by high temperature nitridation of either Ga-Zn-hydroxide-like precipitates obtained from nitrates or mixtures of Ga2O3 and ZnO.
  • A combination of bulk and surface characterization methods revealed that irrespective to the starting material, the product of the synthesis was a wurtzite-like Ga-Zn-oxynitride phase.
  • This transformation became complete during the photocatalytic methanol reforming reaction, accompanied by reduction of the Pt co-catalyst until the fully metallic state.
  • Eventually, it was demonstrated that Pt was an effective catalyst in surface transformation of the oxynitride to oxyhydroxide both by thermal and photo activated processes.
  • The finding that, irrespectively to synthesis routes of the photocatalyst, metallic Pt- loaded Ga-Zn-oxyhydroxide formed under the reaction conditions suggests that this Ptoxyhydroxide system could play an important role in the photocatalytic reaction.

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Journal ArticleDOI
TL;DR: Wurtzite Zinc-gallium oxynitrides (ZnGaNO) particles were synthesized by nitridation of Zn/Ga/CO3 layered double hydroxides (LDHs) using three different coprecipitation methods, called Decreasing-pH method, Constant-p H method, and Increasing-PH Method, respectively as discussed by the authors.

20 citations

Journal ArticleDOI
TL;DR: Platinum was more easily reducible in all of the P25 supported samples compared to those obtained from the more water-retentive homemade TiO2 and the highest H2 evolution rate was observed over P25 based samples and the H2 treatment resulted in more active samples than the other co-catalyst formation methods.
Abstract: In this study, relationships between preparation conditions, structure, and activity of Pt-containing TiO₂ photocatalysts in photoinduced reforming of glycerol for H₂ production were explored. Commercial Aerolyst® TiO₂ (P25) and homemade TiO₂ prepared by precipitation-aging method were used as semiconductors. Pt co-catalysts were prepared by incipient wetness impregnation from aqueous solution of Pt(NH₃)₄(NO₃)₂ and activated by calcination, high temperature hydrogen, or nitrogen treatments. The chemico-physical and structural properties were evaluated by XRD, ¹H MAS NMR, ESR, XPS, TG-MS and TEM. The highest H₂ evolution rate was observed over P25 based samples and the H₂ treatment resulted in more active samples than the other co-catalyst formation methods. In all calcined samples, reduction of Pt occurred during the photocatalytic reaction. Platinum was more easily reducible in all of the P25 supported samples compared to those obtained from the more water-retentive homemade TiO₂. This result was related to the negative effect of the adsorbed water content of the homemade TiO₂ on Pt reduction and on particle growth during co-catalyst formation.

17 citations


Cites background from "Structural evolution in Pt/Ga-Zn-ox..."

  • ...In case of co-catalyst formation by calcination, in situ reduction of platinum has been found during the photoinduced H2 production from methanol-water reaction mixture [29,42]....

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  • ...formation by calcination was favorable for the hydrogen production in the photocatalytic reaction of methanol [29,42]....

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Journal ArticleDOI
TL;DR: In this article, a graphite-oxide/TiO2 composite material was prepared by heterocoagulation method from Brodie's graphiteoxide (GO) in order to test them as catalysts in the methanol photocatalytic reforming reaction in liquid phase.
Abstract: Graphite-oxide/TiO2 (GO/TiO2) composite materials were prepared by heterocoagulation method from Brodie’s graphite-oxide (GO) in order to test them as catalysts in the methanol photocatalytic reforming reaction in liquid phase. The preparation of the composite itself resulted in only little changes in the structure of GO as it was indicated by attenuated total reflection infrared (ATR-IR) and 13C magic-angle spinning nuclear magnetic resonance (13C MAS NMR) spectroscopic measurements. However, during the photocatalytic reaction, all of the GO/TiO2 samples darkened strongly indicating structural changes of GO. X-ray photoelectron spectroscopy along with NMR confirmed the loss of oxygen functionalities and emergence of graphitic species in the samples recovered from the photocatalytic reaction. Model experiments were designed to identify the key factors determining the activity of the GO/TiO2 derived photocatalysts. It was found that the emergence of a pronounced coupling between TiO2 and the graphite-like carbonaceous material is the most important contribution to get active and stable photocatalysts.

12 citations


Cites background from "Structural evolution in Pt/Ga-Zn-ox..."

  • ...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....

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Journal ArticleDOI
TL;DR: A broad overview of the development of photocatalysts for the generation of H2 and CO2 reduction reaction, summarizing the current state of work focusing on the recent progress in light-induced overall water splitting and CO 2 reduction on metal nitride photocatalyst.
Abstract: Recently, metal nitrides (MNs) have received renewed attention due to their potential as catalytic materials in energy transformations, with water spitting and CO2 reduction being the most studied reactions Reactions considered in this review are limited to photocatalysis Moreover, the morphology, size, defects and nanostructured construction of MNs are demonstrated to be critical factors in their catalytic efficiency, emphasizing the importance of their synthetic method Mono, binary, ternary and doped nanostructured MN materials have been synthesized and evaluated as photocatalysts The latest research is focused on the development of new synthetic methods, cocatalysts, and constructure design, aiming to achieve improved activity, selectivity, and stability This review provides a broad overview of the development of photocatalysts for the generation of H2 and CO2 reduction reaction, summarizing the current state of work focusing on the recent progress in light-induced overall water splitting and CO2 reduction on metal nitride photocatalysts

11 citations

Journal ArticleDOI
TL;DR: The synthesis presented here allows the preparation of small nanoparticles (less than 20 nm in diameter), well-defined in size and shape, yet highly crystalline and the highest surface area reported so far (up to ~80 m 2 /g).
Abstract: A versatile synthetic strategy for the preparation of multimetallic oxynitrides has been designed and here exemplarily discussed considering the preparation of nanoscaled zinc-gallium oxynitrides and zinc-gallium-indium oxynitrides, two important photocatalysts of new generation, which proved to be active in key energy related processes from pollutant decomposition to overall water splitting. The synthesis presented here allows the preparation of small nanoparticles (less than 20 nm in average diameter), well-defined in size and shape, yet highly crystalline and with the highest surface area reported so far (up to 80 m2 g-1 ). X-ray diffraction studies show that the final material is not a mixture of single oxides but a distinctive compound. The photocatalytic properties of the oxynitrides have been tested towards the decomposition of an organic dye (as a model reaction for the decomposition of air pollutants), showing better photocatalytic performances than the corresponding pure phases (reaction constant 0.22 h-1 ), whereas almost no reaction was observed in absence of catalyst or in the dark. The photocatalysts have been also tested for H2 evolution (semi-reaction of the water splitting process) with results comparable to the best literature values but leaving room for further improvement.

8 citations

References
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TL;DR: In this article, the authors focus on interfacial processes and summarize some of the operating principles of heterogeneous photocatalysis systems, including the electron transfer and energy transfer processes in photocatalytic reactions.
Abstract: In 1972, Fujishima and Honda discovered the photocatalytic splitting of water on TiO{sub 2} electrodes. This event marked the beginning of a new era in heterogeneous photocatalysis. Since then, research efforts in understanding the fundamental processes and in enhancing the photocatalytic efficiency of TiO{sub 2} have come from extensive research performed by chemists, physicists, and chemical engineers. Such studies are often related to energy renewal and energy storage. In recent years, applications to environmental cleanup have been one of the most active areas in heterogeneous photocatalysis. This is inspired by the potential application of TiO{sub 2}-based photocatalysts for the total destruction of organic compounds in polluted air and wastewaters. There exists a vast body of literature dealing with the electron transfer and energy transfer processes in photocatalytic reactions. A detailed description of these processes is beyond the scope of this review. Here, the authors tend to focus on interfacial processes and to summarize some of the operating principles of heterogeneous photocatalysis. In section 2, the authors first look at the electronic excitation processes in a molecule and in a semiconductor substrate. The electronic interaction between the adsorbate molecule and the catalyst substrate is discussed in terms of the catalyzed ormore » sensitized photoreactions. In section 3, thermal and photocatalytic studies on TiO{sub 2} are summarized with emphasis on the common characteristics and fundamental principles of the TiO{sub 2}-based photocatalysis systems. In section 4, they address the research effort in the electronic modification of the semiconductor catalysts and its effect on the photocatalytic efficiency. Several representative examples will be presented including the Schottky barrier formation and modification at metal-semiconductor interfaces. Some concluding remarks and future research directions will be given in the final section. 160 refs.« less

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Journal ArticleDOI
TL;DR: The research shows that loading suitable dual cocatalysts on semiconductors can significantly increase the photocatalytic activities of hydrogen and oxygen evolution reactions, and even make the overall water splitting reaction possible.
Abstract: Since the 1970s, splitting water using solar energy has been a focus of great attention as a possible means for converting solar energy to chemical energy in the form of clean and renewable hydrogen fuel. Approaches to solar water splitting include photocatalytic water splitting with homogeneous or heterogeneous photocatalysts, photoelectrochemical or photoelectrocatalytic (PEC) water splitting with a PEC cell, and electrolysis of water with photovoltaic cells coupled to electrocatalysts. Though many materials are capable of photocatalytically producing hydrogen and/or oxygen, the overall energy conversion efficiency is still low and far from practical application. This is mainly due to the fact that the three crucial steps for the water splitting reaction: solar light harvesting, charge separation and transportation, and the catalytic reduction and oxidation reactions, are not efficient enough or simultaneously. Water splitting is a thermodynamically uphill reaction, requiring transfer of multiple electrons, making it one of the most challenging reactions in chemistry. This Account describes the important roles of cocatalysts in photocatalytic and PEC water splitting reactions. For semiconductor-based photocatalytic and PEC systems, we show that loading proper cocatalysts, especially dual cocatalysts for reduction and oxidation, on semiconductors (as light harvesters) can significantly enhance the activities of photocatalytic and PEC water splitting reactions. Loading oxidation and/or reduction cocatalysts on semiconductors can facilitate oxidation and reduction reactions by providing the active sites/reaction sites while suppressing the charge recombination and reverse reactions. In a PEC water splitting system, the water oxidation and reduction reactions occur at opposite electrodes, so cocatalysts loaded on the electrode materials mainly act as active sites/reaction sites spatially separated as natural photosynthesis does. In both cases, the nature of the loaded cocatalysts and their interaction with the semiconductor through the interface/junction are important. The cocatalyst can provide trapping sites for the photogenerated charges and promote the charge separation, thus enhancing the quantum efficiency; the cocatalysts could improve the photostability of the catalysts by timely consuming of the photogenerated charges, particularly the holes; most importantly, the cocatalysts catalyze the reactions by lowering the activation energy. Our research shows that loading suitable dual cocatalysts on semiconductors can significantly increase the photocatalytic activities of hydrogen and oxygen evolution reactions, and even make the overall water splitting reaction possible. All of these findings suggest that dual cocatalysts are necessary for developing highly efficient photocatalysts for water splitting reactions.

2,236 citations

Journal ArticleDOI
TL;DR: In this paper, the dependence of the exchange current for the electrolytic evolution of hydrogen on metals (i 0,H ) on the work function is analyzed on the basic of a new list of polycrystalline surfaces.

1,474 citations

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Q1. What are the contributions in "Structural evolution in pt/ga-zn-oxynitride catalysts for photocatalytic reforming of methanol" ?

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