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Graphical abstract Highlights • Galvanic replacement (GR) reactions between Co/SiO 2 and Pt2+or Pt2+ and Ir3+ cations are employed to prepare Pt-Co/SiO 2 and Pt-Ir-Co/SiO 2 catalysts. • The GR preparation ensures selective deposition of Pt or/and Ir atoms on the Co surface, creating highly exposed Pt or/and Ir clusters on Co NPs. • The catalysts prepared by GR show superior performance for the title reaction to their counterparts prepared by impregnation. • Pt-Ir-Co/SiO 2 presents the highest activity and yield for producing the ring-opening products, uncovering a synergistic effect between Pt and Ir. • Advantage of the GR preparation is demonstrated for preparing noble-metal-efficient catalysts. Abstract Pt-Co/SiO 2 and Pt-Ir-Co/SiO 2 catalysts were prepared via galvanic replacement (GR) and employed for the hydrogenolytic ring-opening of methylcyclopentane (MCP). Selective deposition of the noble metals at the less expensive Co nanoparticle (NP) surface by GR greatly enhanced the utilization efficiency of the more active Pt or Pt and Ir atoms for the selective catalysis to the ring-opening reaction of MCP, as justified by comparison with catalysts from conventional impregnation preparation. The chemistry of GR was quantitatively studied by comprehension of the composition changes both in the preparation solution and in the solid samples. The structural features of GR catalysts were characterized as highly dispersed Pt or Pt and Ir clusters selectively deposited on Co NP surface. Compared to their counterparts from impregnation preparation, the GR catalysts showed much higher mass-specific activity normalized by overall noble metal loading (MSA NM), due to the significantly enhanced utilization efficiency of Pt or Pt and Ir. In addition, the trimetallic Pt-Ir-Co/SiO 2 catalyst showed a distinctly higher MSA NM than the bimetallic Pt-Co/SiO 2 and Ir-Co/SiO 2 ones. This observation features a synergy between the highly dispersed Pt and Ir clusters in the catalysis, besides the enhanced noble metal utilization efficiency. Our catalytic data seem to suggest that a dicarbene mechanism was prevailing over the GR catalysts for the ring-opening reaction of MCP. [ABSTRACT FROM AUTHOR]

The direct redox reaction (galvanic displacement) between Pd2+ and substrate Si was used to deposit Pd on Si, and the Pd–Si catalysts enabled a chemoselective hydrogenation of para-chloronitrobenzene with the selectivity for para-chloroaniline higher than 99.9% at complete conversion of para-chloronitrobenzene. [ABSTRACT FROM AUTHOR]

Adding a very small amount of Pt entities (0.01–0.03 wt%) onto the Au surface of a Au/TiO2 catalyst is found to be an efficient approach to improve the catalytic activity of Au for the hydrogenation of p-chloronitrobenzene (p-CNB), without loss of selectivity towards p-chloroaniline (p-CAN). The effect of catalyst amount, reaction temperature, H2 pressure and reaction time on p-CNB hydrogenation was studied with 0.02wt%Pt–0.5wt%Au/TiO2 (Pt0.0002–Au0.005/TiO2). The selectivity to p-CAN could be up to 100% at complete conversion of p-CNB with reaction temperatures at or below 333 K. The catalyst also exhibited perfect stability. The catalyst structure was characterized by TEM and XRD, and the mechanism of the high activity of the catalyst was discussed. [ABSTRACT FROM AUTHOR]

Adding a small amount of fully dispersed Pt entities onto the Au surface in Au/SiO2catalyst is found to be an efficient approach to improve the catalytic activity of Au (up to 70-fold) for the hydrogenation of α,β-unsaturated carbonyl compounds, without alternating its selectivity towards CO or CC bond hydrogenation. [ABSTRACT FROM AUTHOR]

Abstract: Hydrogenation of 1,3-butadiene over Au/ZrO2 catalysts with different gold loadings and calcination temperatures was reported. The catalysts were characterized in depth to understand their structure–property relationship. Gold oxidation states and surface hydroxyl groups, which were found to be sensitive to the gold loading, calcination temperature, and treatment with water, were shown to play vital roles in the hydrogenation activity of Au/ZrO2. Continued activity decrease was seen when the density of surface hydroxyl groups was lowered by elevating the pre-calcination temperature of ZrO2. Fully dehydroxylated Au/ZrO2 was essentially inactive, but became very active after partial regeneration of the hydroxyl groups by water treatment. Moreover, the activity of Au/ZrO2 increased with increasing Au3+/Au0 ratio. Isolated Au3+ ions at the support surface showed up to two orders of magnitude higher activity than Au0 atoms on Au particles. Several models are proposed to address the structural features of active sites for H2 activation in Au/ZrO2 catalysts. [Copyright &y& Elsevier]

Abstract: This work investigates the effects of Au3+/Au0 ratio or distribution of gold oxidation states in Au/ZrO2 catalysts of different gold loadings (0.01–0.76% Au) on CO oxidation and 1,3-butadiene hydrogenation by regulating the temperature of catalyst calcination (393–673K) and pre-reduction with hydrogen (473–523K). The catalysts were prepared by deposition–precipitation and were characterized with elemental analysis, nitrogen adsorption/desorption, TEM, XPS and TPR. The catalytic data showed that the exposed metallic Au0 atoms at the surface of Au particles were not the only catalytic sites for the two reactions, isolated Au3+ ions at the surface of ZrO2, such as those in the catalysts containing no more than 0.08% Au were more active by TOF. For 0.76% Au/ZrO2 catalysts having coexisting Au3+ and Au0, the catalytic activity changed differently with varying the Au3+/Au0 ratio in the two reactions. The highest activity for the CO oxidation reaction was observed over the catalyst of Au3+/Au0 =0.33. However, catalyst with a higher Au3+/Au0 ratio showed always a higher activity for the hydrogenation reaction; co-existance of Au0 with Au3+ ions lowered the catalyst activity. Moreover, the coexisting Au particles changed the product selectivity of 1,3-butadiene hydrogenation to favor the formation of more trans-2-butene and butane. It is thus suggested that for better control of the catalytic performance of Au catalyst the effect of Au3+/Au0 ratio on catalytic reactions should be investigated in combination with the particle size effect of Au. [Copyright &y& Elsevier]

Abstract: This work reports for the first time an “unusual” property of immobilized PVA-stabilized gold nanoparticles (AuNPs) on SiO2 for highly selective hydrogenation at the C cinnamaldehyde (CAL) at 150–180°C, uncovering a catalytic route for selective hydrocinnamaldehyde (HCAL) production from CAL. When the same colloidal gold nanoparticles are immobilized on ZrO2, they effect competitive hydrogenations at both Ce:glyph name="dbnd" />O bonds of the CAL molecules under identical reaction conditions. [Copyright &y& Elsevier]