Dendrimer-Encapsulated Pd Nanoparticles, Immobilized in Silica Pores, as Catalysts for Selective Hydrogenation of Unsaturated Compounds

Heterogeneous Pd-containing nanocatalysts, based on poly (propylene imine) dendrimers immobilized in silica pores and networks, obtained by co-hydrolysis in situ, have been synthesized and examined in the hydrogenation of various unsaturated compounds. The catalyst activity and selectivity were found to strongly depend on the carrier structure as well as on the substrate electron and geometric features. Thus, mesoporous catalyst, synthesized in presence of both polymeric template and tetraethoxysilane, revealed the maximum activity in the hydrogenation of various styrenes, including bulky and rigid stilbene and its isomers, reaching TOF values of about 230000 h-1. Other mesoporous catalyst, synthesized in the presence of polymeric template, but without addition of Si(OEt)4, provided the trans-cyclooctene formation with the selectivity of 90-95 %, appearing as similar to homogeneous dendrimer-based catalysts. Microporous catalyst, obtained only on the presence of Si(OEt)4, while dendrimer molecules acting as both anchored ligands and template, demonstrated the maximum activity in the hydrogenation of terminal linear alkynes and conjugated dienes, reaching TOF values up to 400000 h-1. Herein the total selectivity on alkene in the case of terminal alkynes and conjugated dienes reached 95-99 % even at hydrogen pressure of 30 atm. The catalysts synthesized can be easily isolated from reaction products and recycled without significant loss of activity.

Unraveling sorption of nickel from aqueous solution by KMnO4 and KOH-modified peanut shell biochar: Implicit mechanism

Nickel-containing wastewater is a serious hazard to water environment, so that it is a burning issue to find an efficient and environment-friendly adsorbent. The conventional biochar could not effectively adsorb nickel (Ni(II)), so our study focuses on exploring the adsorption of chemically modified biochar to Ni(II). In this study, the biochar derived from waste peanut shell was modified by KMnO₄ and KOH (MBC). And a series of experiment were carried out to evaluate the sorption ability and explore adsorption mechanism of modified biochar to Ni(II). The results showed the adsorption ability of MBC to Ni(II) reached 87.15 mg g^-1. And the reaction process was spontaneous and endothermic chemisorption. Meanwhile, the analysis of FTIR and XPS visually revealed that the amine groups in the modified biochar could form NH₂Ni with Ni(II) by complexation, while the hydroxyl could form nickel hydroxide and complexed nickel oxide by co-precipitation and complexation. This research showed this novel MBC is a promising adsorbent and has a fantastic prospect in the application of nickel-containing wastewater.

Thermal reduction of Pd molecular cluster precursors at highly ordered pyrolytic graphite surfaces

Highly ordered pyrolytic graphite (HOPG) surfaces were modified by the adsorption of Pd molecular precursors from solution. Two palladium-containing molecular precursors were studied, a mononuclear one and a trinuclear one, to compare their affinities and distributions at substrate surfaces. To obtain Pd nanoparticles, these neutral molecular precursors were reduced under a hydrogen atmosphere. Thermogravimetric analysis was carried out to establish the behavior of these precursors at various temperatures. Understanding the thermal stability of these compounds is very important to establish the appropriate conditions to form metallic Pd. The modified surface has been characterized by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy; also, the reductive process was monitored by XPS. Remarkable differences were observed between the mononuclear and trinuclear compounds in terms of dispersion, particle size, and homogeneity. The preference of the trinuclear compound was to deposit at HOPG defects, in contrast to that of the mononuclear one, which was agglomeration on all surfaces. After the application of this technique, not only Pd nanoparticles but also Pd nanowires were obtained.

Halogen-Bridged Mixed-Valence Linear-Chain Complexes: Molecular Orbital Model of Electron Localization

A simple tight-binding model is used to study electronic distributions and Peierls distortions in a series of mixed-valence linear-chain complexes [M(II)(LL)(2)][M(IV)(LL)(2)X(2)] (M = Ni, Pd, Pt; X = Cl, Br, I; LL = 1,2-diaminoethane, 1,3-diaminopropane). The calculated values of Peierls distortions for complexes with known structure are in good agreement with the experimental data. For the whole series, the model is employed as a qualitative tool to analyze structural and electronic properties. It is shown that charge disproportionation occurs in the related dimers. Thus, our quantum chemical calculations as well as previous phenomenological approaches indicate that, in metal-halogen chains, one deals with the interplay of local and cooperative effects.