Highly-Ordered PdIn Intermetallic Nanostructures Obtained from Heterobimetallic Acetate Complex: Formation and Catalytic Properties in Diphenylacetylene Hydrogenation

Abstract

Formation of PdIn intermetallic nanoparticles supported on α-Al2O3 was investigated by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and hydrogen temperature-programmed desorption (H2-TPD) methods. The metals were loaded as heterobimetallic Pd(μ-O2CMe)4In(O2CMe) complex to ensure intimate contact between Pd and In. Reduction in H2 at 200 °C resulted in Pd-rich PdIn alloy as evidenced by XRD and the disappearance of Pd hydride. A minor amount of Pd1In1 intermetallic phase appeared after reduction at 200 °C and its formation was accomplished at 400 °C. Neither monometallic Pd or in nor other intermetallic structures were found after reduction at 400–600 °C. Catalytic performance of Pd1In1/α-Al2O3 was studied in the selective liquid-phase diphenylacetylene (DPA) hydrogenation. It was found that the reaction rate of undesired alkene hydrogenation is strongly reduced on Pd1In1 nanoparticles enabling effective kinetic control of the hydrogenation, and the catalyst demonstrated excellent selectivity to alkene.

Local Structure of Pd1 Single Sites on the Surface of PdIn Intermetallic Nanoparticles: A Combined DFT and CO-DRIFTS Study

“…Similar observations were presented elsewhere [33,34]. Results of our previous CO-DRIFTS study of Pd 1 In 1 /Al 2 O 3 are in good agreement with these data and demonstrate the disappearance of multiply-bonded CO species on the surface of PdIn nanoparticles [18,30,35]. However, it is still unclear which characteristic features of PdIn surface structure impede the multipoint adsorption of CO.…”

“…Figure 1 [29,36,37]. For the Pd/Al 2 O 3 catalyst, a characteristic peak was observed at 40.2 and a noticeable reflex at 46.7 attributed to the (111) and (200) facets of Pd, respectively (ICSD N • 180870) [18,31,38].…”

“…Note that bridged and threefold hollow-bonded CO adsorption is energetically more favorable than linear CO adsorption on Pd surface [24,25] and usually the signals of multiply coordinated CO tend to prevail in infrared spectra. Therefore, convincing evidence of the formation of Pd 1 single-site surface structure is the complete disappearance of bridged and triple bonded CO adsorption signals and the presence of linearly bonded CO only, suggesting that CO coordination to several Pd atoms is unfavorable [18][19][20][26][27][28][29][30][31][32].…”

“…An excellent example of single-site intermetallic catalyst is PdIn compositions, which demonstrate a favorable performance for selective semihydrogenation of substituted alkynes, direct formic acid fuel cell processes, production of enhanced magnetic resonance signals using parahydrogen, etc. [17][18][19][20][21]. The specific catalytic properties of PdIn IMCs are attributed to the formation of single Pd 1 sites on their surface, isolated from each other by indium atoms [12,17,20,22,23], which prevents or hinders multipoint adsorption of reacting molecules.…”

Organic–Inorganic Hybrid Nanomaterials

“…Catalytic systems can be significantly improved by the advantageous application of hybrid structures. Intermetallic PdIn nanoparticles were supported on alumina, giving a Pd 1 In 1 /α-Al 2 O 3 catalyst, which was evaluated for selective liquid-phase hydrogenation of diphenylacetylene [50]. Efficient kinetic control of the hydrogenation process and excellent reaction selectivity were observed.…”