Synthesis of Titania-Supported Platinum Catalyst:  The Effect of pH on Morphology Control and Valence State during Photodeposition

Abstract

Solid-supported metal catalysts have been widely used in industrial processes. The morphology of coated metal on the support is usually an important factor affecting the efficiency of the catalyst. In this study, a photocatalytic process is utilized to control the morphology of platinum particles deposited on titania (Degussa P-25). More specifically, the effect of pH on the morphology and the valence state of platinum nanoparticles was systemically investigated. It is found that, via a simple pH-controlled process, various states of platinum (Pt0, PtIIO, or PtIVO2) can be deposited onto the support directly at will. In this paper, the mechanism of morphology control and the key influencing factors at different pH regimes will be discussed. Followed by photodeposition, a H2 thermal treatment process was employed to convert the oxides into metal platinum with narrow size distribution and even coverage on the supporting titania. Various techniques such as transmission electron microscopy, high-resolution transmission electron microscopy, energy-dispersive analysis of X-rays, and X-ray photoelectron spectroscopy were employed to characterize the prepared titania-supported platinum particles.

Relations between Structure, Activity and Stability in C3N4 Based Photocatalysts Used for Solar Hydrogen Production

“…The surface composition of the Pt NPs in the various catalysts treated in TEOA does not differ much. All NPs contain metallic Pt 0 besides oxidized Pt 2+ , reflected by Pt 4f 7/2 peaks at 70-72 eV and 74 eV, respectively [19] (Figure 3c). Especially in the AIS-containing samples, these peaks are very broad, making a meaningful deconvolution into distinct doublets for 4f 7/2 and 4f 5/2 difficult.…”

“…This is probably due to the fact that not the whole amount of the solved [PtCl 6 ] 2− precursor but only a part of it is reduced and deposited as Pt NPs in basic TEOA solution. It has been shown that at high pH (as in the presence of TEOA) a stepwise hydrolysis occurs according to [PtCl 6 ] 2− → [Pt(OH) x Cl 6−x ] 2− → [Pt(OH) 6 ] 2− which hampers the formation of metallic Pt particles [19]. Moreover, the rather non-polar surface of CN might be less prone than the polar AIS surface to adsorb the polar Pt complex species.…”

“…However, the total Pt content as well as the surface Pt percentage of the Pt/CN catalyst are much higher in OA than in TEOA, which might lead to higher activity (Table 1). This is most probably due to the fact that direct reduction of [PtCl 6 ] 2− to metallic Pt is facilitated at low pH; intermediate hydrolysis of the Pt precursor complex, as in basic medium, is avoided [19]. No deactivation of the Pt/CN catalyst occurs in the presence of OA.…”

Nanostructured Heterogeneous Catalysts: Well Defined Platinum Nanoparticles Supported on Alumina. Preparation, Characterization and Application to the Selective Hydrogenation of Buta-1,3-diene

“…CTAB probably forms micellar species since its concentration in solution (around 5 mM in the final solution) is higher than the Critical Micellar Concentration (0.8-1.1 mM) [37]. When the aged H 2 PtCl 6 solution is added, the Pt 4+ cation could be surrounded by different coordination shells since the ageing of the solution is supposed to lead to the partial or complete substitution of chloride ligands by hydroxides ones [21,22,38]: (1), an interaction between CTAB and the platinate salt could be envisaged. Such an interaction could lead to {Pt 4+ -CTAB} moieties as it was previously demonstrated for palladium [14].…”

Synthesis of TiO2 and SiO2 Oxide Systems, Containing Nanoparticles of Palladium and Platinum

“…Materials based on titanium dioxide are well known for the pronounced catalytic and photocatalytic properties [1][2][3][4][5][6][7] . Presence of metallic nanoparticles formed of platinum group metals in oxide systems based on titanium dioxide, often leads to increased catalytic activity [8][9][10][11][12] .…”