Hollow PdAg-CeO2 heterodimer nanocrystals as highly structured heterogeneous catalysts

Abstract

In the present work, hollow PdAg-CeO2 heterodimer nanocrystals (NCs) were prepared and tested as catalysts for the selective hydrogenation of alkynes. These nanostructures combine for the first time the beneficial effect of alloying Pd with Ag in a single NC hollow domain with the formation of active sites at the interface with the CeO2 counterpart in an additive manner. The PdAg-CeO2 NCs display excellent alkene selectivity for aliphatic alkynes. For the specific case of hydrogenation of internal alkynes such as 4-octyne, very low over-hydrogenation and isomerization products were observed over a full conversion regime, even after prolonged reaction times. These catalytic properties were remarkably superior in comparison to standard catalysts. The promotion of Ag on the moderation of the reactivity of the Pd phase, in combination with the creation of interfacial sites with the CeO2 moiety in the same nanostructure, is pointed as the responsible of such a remarkable catalytic performance.

Ceria-Based Catalysts Studied by Near Ambient Pressure X-ray Photoelectron Spectroscopy: A Review

“…These factors are interdependent and originate complex systems. As expected, the electronic state of the deposited metal nanoparticles strongly depends on the reduction degree of the ceria support and, in particular, by the presence of oxygen vacancies in areas underneath the metal [41,42]. Interestingly, the presence of metal nanoparticles on top of ceria crystallites in turn strongly modifies the reducibility of the underlying cerium oxide.…”

Co3S4 Nanoplate Arrays Decorated with Oxygen-Deficient CeO2 Nanoparticles for Supercapacitor Applications

“…38 Moreover, the rich heterointerfaces between CeO 2 NPs and Co 3 S 4 -NPA result in a strong electronic coupling effect (as confirmed by XPS), giving rise to more defects. 39 In addition, the nonstoichiometric ratio of Ce to O (1:1.4) confirmed by EDS (Figure S3) also suggests the presence of oxygen vacancies.…”

“…As shown in Figure , a signal peak at g = 2.003 appears on Co 3 S 4 /CeO 2 -NPAs and Co 3 S 4 -NPAs, corresponding to unmatched electrons in oxygen vacancies. , Notably, Co 3 S 4 /CeO 2 -NPAs have a stronger peak signal than that of Co 3 S 4 -NPAs, suggesting that Co 3 S 4 /CeO 2 -NPAs contain more oxygen vacancies, since CeO 2 itself is oxygen vacancy-rich . Moreover, the rich heterointerfaces between CeO 2 NPs and Co 3 S 4 -NPA result in a strong electronic coupling effect (as confirmed by XPS), giving rise to more defects . In addition, the nonstoichiometric ratio of Ce to O (1:1.4) confirmed by EDS (Figure S3) also suggests the presence of oxygen vacancies.…”

Synthetic Approaches to Colloidal Nanocrystal Heterostructures Based on Metal and Metal-Oxide Materials

“…A general synthetic procedure involves the thermal decomposition of metalorganic compounds or metal carboxylate complexes as the precursors in the presence of pre-synthesized metal, metal alloyFe 3 O 4 or FePt seeds in a liquid environment composed of a solvent (typically, ODE or phenyl ether) loaded with selected surfactants (usually, OLAC, OLAM and/or TOP) at 200–300 °C. Such a scheme has enabled access to hetero-dimer CNHSs with epitaxially bound domains with close-to-spherical and/or cubic shape, such as of Au–Fe 3 O 4 , AuAg–Fe 3 O 4 , PtPd–Fe 3 O 4 , AuPd–Fe 3 O 4 , AuPt–Fe 3 O 4 , AuCu–Fe 3 O 4 , Pt–Fe 3 O 4 , Ni–Fe 3 O 4 , Cu–Fe 3 O 4 , Ru–Fe 3 O 4 , Au–CoO, AuAg–CoO, Pt–CoO, Au–MnO, Ag–MnO, FePt–CoFe 2 O 4 , FePt–In 2 O 3 , FePt–Fe 3 O 4 , FePt–MgO, Au–In:CdO, FePt–In:CdO, Pt–In:CdO, Pd–In:CdO, Cu–CeO 2 , Cu–ZrO 2 and Cu–ZnO [ 99 , 218 , 219 , 224 , 230 , 231 , 232 , 233 , 234 , 237 , 238 , 239 , 241 , 242 , 243 , 244 , 245 , 246 , 247 , 248 , 249 , 250 , 251 , 252 , 253 , 254 , 255 , 256 , 257 , 258 , 259 , 260 , 261 ,…”

“…These observations are perfectly congruent with the participation of a de-wetting event in the early formation stages of the CNHSs, as described above. Other types of solid/hollow hetero-dimer CNCs were derived by performing chemical reactions (for example, sulfidation or etching and transmetalation) on either section of metal/metal-oxide hetero-dimer CNHSs [ 260 , 261 ].…”