Thermal and surface analysis of palladium pyrazolates molecular precursors

Abstract

The reduction of molecular or ionic precursors represents one of the more suitable and effective methods to obtain small and uniform particles. In the present work, various palladium (Pd(II)) molecular precursors (MPs) were characterized before and after thermal reduction process, as an alternative to form Pd nanoparticles. These MPs are classified in two principal groups; those that contain 3,5-dimethylpyrazole and those that contain 3-phenyl or 3,5-diphenyl pyrazole with some chemical variations: Pd(3,5-Ph2pzH)2Cl2 (MP(I)), Pd(3-PhpzH)2Cl2 (MP(II)), Pd(3,5-Me2pzH)2Cl2 (MP(III)), Pd(4-Br-3,5-Me2pzH)2Cl2 (MP(IV)), Pd2(µ-3,5-Ph2pz)2(3,5-Ph2pzH)2Cl2·H2O (MP(V)), Pd2(µ-3,5-Me2pz)2(3,5-Me2pzH)2Cl2 (MP(VI)), and Pd3(µ-Phpz)6 (MP(VII)). In order to obtain Pd nanoparticles, these neutral MPs were reduced under hydrogen atmosphere. Thermogravimetric analyses were carried out to establish the thermal stability of these compounds, an important parameter in order to select the appropriate conditions to form metallic Pd nanoparticles. To confirm the reduction of the precursors, Fourier transformed infrared (FT-IR) and X-ray photoelectron spectroscopy (XPS) analysis were performed on the molecular cluster precursor powders. The present study is a preparatory guide to establish the appropriate conditions in order to promote the formation of Pd nanoparticles. The temperature of 600 °C emerges as an ideal temperature to reach the decomposition of organic groups in the Pd(II) MPs, as well as the formation of metallic Pd particles, as corroborated by FT-IR and XPS analysis. These Pd MPs represent a new alternative for the preparation of metallic Pd nanoparticles.