Supported Au25 clusters were prepared through the calcination of Au25(SC12H25)18 on hierarchically porous carbon nanosheets under vacuum at temperatures in the range of 400–500 °C for 2–4 h. TEM and EXAFS analyses revealed that the thiolate coverage on Au25 gradually decreased with increasing calcination temperature and period and became negligibly small when the calcination temperature exceeded 500 °C. The catalysis of these Au25 clusters was studied for the aerobic oxidation of benzyl alcohol. Interestingly, the selectivity for benzaldehyde formation was remarkably improved with the increase in the amount of residual thiolates on Au25, while the activity was reduced. This observation is attributed to the dual roles of the thiolates: the reduction of the oxidation ability of Au25 by electron withdrawal and the inhibition of the esterification reaction on the cluster surface by site isolation.

The development of novel catalysts based on metal clusters requires a rational design principle as well as atomically precise synthetic methods. Toward this goal, we have developed a method to precisely and independently control the size, composition, and surface modification of heterogeneous gold clusters by calcination of the ligand-protected Au clusters on carbon supports. We studied the effects of these structural parameters using benzyl alcohol oxidation as a test reaction. Unexpectedly, Au and Au on hierarchically porous carbon exhibited significantly higher turnover frequency than Au and Au . This size dependence is ascribed to the difference in the geometric structures of the Au clusters; Au and Au have an icosahedral-based structure whereas Au and Au have a face-centered cubic structure. Doping of a single Pd atom into Au supported on carbon nanotubes remarkably enhanced the catalytic activity. The doping effect is explained in terms of the accelerated formation of the carbocation intermediate due to electron transfer from Pd to Au, since the doped Pd is buried within the Au clusters and is located at the interface between the supports. Residual thiolates on Au affected both the activity and selectivity; selective oxidation to benzaldehyde was achieved at optimized coverage. Non-formation of benzoic acid is due to the suppression of oxidation activity by electron withdrawal by thiolates and non-formation of benzyl benzoate is due to the site-isolation effect by thiolates. These results will provide useful information for the rational design of gold-cluster-based catalysts with desired performance.

Understanding structural responses of metal-organic frameworks (MOFs) to external stimuli such as the inclusion of guest molecules, temperature/pressure has gained increasing attention in many applications, for example, manipulation and manifesto smart materials for gas storage, energy storage, controlled drug delivery, tunable mechanical properties, and molecular sensing, to name but a few. Herein, neutron and synchrotron diffractions along with Rietveld refinement and density functional theory calculations have been used to elucidate the responsive adsorption behaviors of defect-rich Zr-based MOFs upon the progressive incorporation of ammonia (NH3) and variable temperature. UiO-67 and UiO-bpydc containing biphenyl dicarboxylate and bipyridine dicarboxylate linkers, respectively, were selected and the results establish the paramount influence of the functional linkers on their NH3 affinity, which leads to stimulus-tailoring properties such as gate-controlled porosity by dynamic linker flipping, disorder, and structural rigidity. Despite their structural similarities, we show for the first time the dramatic alteration of NH3 adsorption profiles when the phenyl groups are replaced by the bipyridine in the organic linker. These molecular controls stem from controlling the degree of H-bonding networks/distortions between the bipyridine scaffold and the adsorbed NH3 without significant change in pore volume and unit cell parameters. Temperature-dependent neutron diffraction also reveals the NH3-induced rotational motions of the organic linkers. We also demonstrate that the degree of structural flexibility of the functional linkers can critically be affected by the type and quantity of the small guest molecules. This strikes the delicate control in material properties at the molecular level.

Currently, less favorable C=O hydrogenation and weak concerted acid catalysis cause unsatisfactory catalytic performance in the upgrading of biomass‐derived furfurals (i.e., furfural, 5‐methyl furfural, and 5‐hydroxymethyl furfural) to ketones (i.e., cyclopentanone, 2,5‐hexanedione, and 1‐hydroxyl‐2,5‐hexanedione). A series of partially oxidized MAX phase (i.e., Ti3AlC2, Ti2AlC, Ti3SiC2) supporting Pd catalysts were fabricated, which showed high catalytic activity; Pd/Ti3AlC2 in particular displayed high performance for conversion of furfurals into targeted ketones. Detailed studies of the catalytic mechanism confirm that in situ hydrogen spillover generates Frustrated Lewis H+−H− pairs, which not only act as the hydrogenation sites for selective C=O hydrogenation but also provide acid sites for ring opening. The close intimate hydrogenation and acid sites promote bifunctional catalytic reactions, substantially reducing the reported minimum reaction temperature of various furfurals by at least 30–60 °C.