Hydroxylated surface of GaAs as a scaffold for a heterogeneous Pd catalyst

Abstract

A novel use of GaAs, namely, as a scaffold for a heterogeneous palladium catalyst, is proposed. Hydroxy groups on the GaAs surface play important roles. During the adsorption of Pd(OAc) 2 on the GaAs surface, the hydroxy groups attract Pd(II) species by anion exchange. A subsequent redox reaction proceeds to generate Pd(0) nanoparticles, which are stabilized on the GaAs surface. This process is confirmed by 10 surface-sensitive measurements: diffuse reflection IR spectroscopy and X-ray photoelectron spectroscopy. Moreover, a more bulk-sensitive measurement, hard X-ray photoemission spectroscopy with synchrotron radiation, also supported our considerations. The amounts of Pd(0) nanoparticles on the surface were evaluated by catalytic activity, yield, and recyclability in the Heck reaction, in addition to deposit test.

Sulfur-mediated palladium catalyst immobilized on a GaAs surface

“…On the basis of these findings, together with our previous results, 16 we propose a plausible mechanism for the redox process which produces catalytically active Pd nanoparticles, as shown in Fig. 7.…”

“…16 The role of the hydroxy groups on the GaAs surface is also confirmed for the S-terminated GaAs by FT-IR measurements.…”

“…A similar loss of Pd species was also observed in previous experiments, in which these lost Pd species were dissolved in the solvent and re-deposited on the surface of the test tube. 16 It is confirmed that such re-deposited Pd species act as a source of active Pd for the Heck reaction. A similar change in the intensity ratio is observed for Series S, but is very minor, suggesting little loss of Pd species.…”

Facilitation of the reduction of Pd(II) by the glass surface – Development of a glass-supported palladium catalyst

“…Indeed, when a polypropylene test tube was used instead of a glass test tube, a considerable amount of Pd(II) still remained (PP) even after heating for 3 h. (Figure 2). In the case of RT, palladium acetate was adsorbed only physically on the glass surface [12]. On the other hand, the peak of the Pd(II) species shifted to a lower binding energy when the cover glass was heated at 120 °C.…”

“…A large amount of Pd(II) was converted to Pd(0) after heating for 1 h, and the reduction was almost completed within 3 h. Note that the heating temperature (120°C) was considerably lower than the decomposition temperature of palladium acetate (205°C), which indicates that the surface of the glass assisted the reduction of the palladium species. Indeed, when a polypropylene test tube was used instead of a glass Pd(II) still remained (PP) even Different chemical shifts o the XPS spectra for RT and the of RT, palladium acetate was surface [12]. On the other h shifted to a lower binding ene at 120°C.…”