Au, Pt, and Au−Pt clusters were grown on TiO2(110) at room temperature and studied by scanning tunneling microscopy. For the same metal coverages, the deposition of pure Pt produces smaller clusters and higher cluster densities compared to pure Au because of the greater mobility of Au on the surface. Heating the surface causes greater sintering of the Au clusters compared to Pt; this behavior is explained by the stronger metal−metal bonds for Pt and the fact that atom detachment is the rate-limiting step in cluster sintering. For the deposition of 0.024 ML of Pt followed by 0.072 ML of Au, bimetallic clusters are formed from the nucleation of Au at existing Pt clusters, whereas the reverse order of deposition results in pure Pt clusters and pure Au clusters coexisting on the surface. The presence of Pt in the bimetallic Pt−Au clusters inhibits sintering, and the average size of the clusters after annealing decreases with increasing Pt composition. Low energy ion scattering experiments demonstrate that the deposition of Au on Pt does not produce core−shell structures with Au on top. Bulk thermodynamics predicts that the cluster surfaces should be pure Au, given that the Au surface free energy is lower than that of Pt, and Au and Pt are immiscible at the compositions studied here. However, surface compositions of the Au−Pt clusters are 10−30% richer in Pt compared to the overall compositions for total coverages of 0.10 ML and 25−75% Pt. These results demonstrate that Au and Pt atoms can intermix at room temperature and the surface properties of Au−Pt nanoclusters are different from those of the bulk. Grazing angle X-ray photoelectron spectroscopy experiments show that annealed Au−Pt clusters are covered by reduced titania. Annealing the Au−Pt clusters to temperatures above 600 K induces encapsulation of the clusters, but the presence of Au at the cluster surface decreases the extent of encapsulation compared to that of pure Pt clusters.

The development of porous well-defined hybrid materials (e.g., metal-organic frameworks or MOFs) will add a new dimension to a wide number of applications ranging from supercapacitors and electrodes to "smart" membranes and thermoelectrics. From this perspective, the understanding and tailoring of the electronic properties of MOFs are key fundamental challenges that could unlock the full potential of these materials. In this work, we focused on the fundamental insights responsible for the electronic properties of three distinct classes of bimetallic systems, MM'-MOFs, MM'-MOFs, and M(ligand-M')-MOFs, in which the second metal (M') incorporation occurs through (i) metal (M) replacement in the framework nodes (type I), (ii) metal node extension (type II), and (iii) metal coordination to the organic ligand (type III), respectively. We employed microwave conductivity, X-ray photoelectron spectroscopy, diffuse reflectance spectroscopy, powder X-ray diffraction, inductively coupled plasma atomic emission spectroscopy, pressed-pellet conductivity, and theoretical modeling to shed light on the key factors responsible for the tunability of MOF electronic structures. Experimental prescreening of MOFs was performed based on changes in the density of electronic states near the Fermi edge, which was used as a starting point for further selection of suitable MOFs. As a result, we demonstrated that the tailoring of MOF electronic properties could be performed as a function of metal node engineering, framework topology, and/or the presence of unsaturated metal sites while preserving framework porosity and structural integrity. These studies unveil the possible pathways for transforming the electronic properties of MOFs from insulating to semiconducting, as well as provide a blueprint for the development of hybrid porous materials with desirable electronic structures.

The thermal decomposition of dimethyl methylphosphonate (DMMP) has been studied in ultrahigh vacuum by temperature programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS) on Ni clusters and films deposited on TiO 2 (110). The four different Ni surfaces under investigation consisted of small Ni clusters (5.0 ( 0.8 nm diameter, 0.9 ( 0.2 nm height) deposited at room temperature and quickly heated to 550 K, large Ni clusters (8.8 ( 1.4 nm diameter, 2.3 ( 0.5 nm height) prepared by annealing to 850 K, a 50 monolayer Ni film deposited at room temperature, and a 50 monolayer Ni film annealed to 850 K. The morphologies of the Ni surfaces were characterized by scanning tunneling microscopy (STM). TPD experiments show that CO and H 2 are the major gaseous products evolved from the decomposition of DMMP on all of the Ni surfaces, and molecular DMMP and methane desorption were also observed. The product yields for CO and H 2 were highest for reactions on the small Ni clusters and unannealed Ni film and lowest for reactions on the large clusters and annealed film. Furthermore, XPS experiments demonstrate that the unannealed Ni surfaces decompose a greater fraction of DMMP at room temperature. The loss of activity for the annealed surfaces is not caused by a reduction in surface area because the annealed surfaces have approximately the same surface area as the small clusters. CO adsorption studies suggest that the loss of activity upon annealing cannot be completely due to a decrease in surface defects, such as step and edge sites, and we propose that a TiO x moiety is responsible for blocking active sites on the annealed Ni surfaces. In comparison to the TiO 2 surface, the small Ni clusters are more chemically active because a greater fraction of DMMP decomposes at room temperature, and the total amount of DMMP decomposition is also higher on the small Ni clusters. Although DMMP decomposes on TiO 2 to produce gaseous methyl radicals, methane, and H 2 , the activity of the substrate surface itself appears to be quenched in the presence of the Ni clusters and films. However, the TiO 2 support plays a significant role in providing a source of oxygen for the recombination of atomic carbon on Ni to form CO, which desorbs above 800 K.

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The growth, surface composition, and chemical activity of bimetallic Pt-Au clusters on TiO 2 (110) have been investigated. Scanning tunneling microscopy (STM) experiments demonstrate that the deposition of Au on Pt clusters results in the formation of bimetallic Pt-Au clusters due to the seeding of the mobile Au atoms at existing Pt nuclei. The composition of the top surface layer of the clusters was studied by low energy ion scattering (LEIS) for bulk compositions ranging from 25%-87.5% Pt with total metal coverages of 0.25 and 0.50 ML. For both coverages, the cluster surfaces consisted of nearly pure Au at Pt compositions of 50% and lower; however, a mix of Au and Pt atoms were found at the cluster surfaces at higher fractions of deposited Pt. These results are consistent with bulk thermodynamics, which predicts a Pt core-Au shell structure based on the lower surface free energy of Au compared to Pt and the large bulk miscibility gap for the two metals. The adsorption of CO on the Pt-Au clusters at room temperature promotes the diffusion of Pt to the surface of the clusters, and this phenomena is most pronounced for the clusters that are initially pure Au at the surface. Density functional theory calculations demonstrate that it is thermodynamically favorable for Pt to diffuse to the cluster surface in order to bind to CO. In contrast, the extent of CO 2 production via sequential adsorption of O 2 and CO on the Pt-Au clusters reflects the surface Pt content before adsorption. For CO oxidation, the first step in the reaction is the dissociation of O 2 at Pt sites. Since this process requires more than one contiguous Pt site, it is not surprising that O 2 dissociation cannot occur on the Pt-Au clusters that are ∼100% Au at the surface before CO exposure, given the low probability for ensembles of Pt sites to form at the surface.

Artificial photosynthesis represents one of the great scientific challenges of the 21 st century, offering the possibility of clean energy through water photolysis and renewable chemicals through CO 2 utilisation as a sustainable feedstock. Catalysis will undoubtedly play a key role in delivering technologies able to meet these goals, mediating solar energy via excited generate charge carriers to selectively activate molecular bonds under ambient conditions. This review describes recent synthetic approaches adopted to engineer 10 nanostructured photocatalytic materials for efficient light harnessing, charge separation and the photoreduction of CO 2 to higher hydrocarbons such as methane, methanol and even olefins. 65 manufacture involves steam or catalytic cracking of naphtha, gasoil and condensates to hydrocarbon mixtures followed by distillation. Cracking crude oil to produce ethene or propene is thermodynamically unfavourable (∆G ≈ +100 kJmol -1 ), requiring high temperatures (> 600°C) to overcome the huge activation 70 barriers to C-C cleavage (280 kJmol -1 for kerosene conversion 29 ). Hence steam cracking is the most energyconsuming process in chemistry, accounting for 8% of the sector's primary energy use and annual CO 2 emissions of 180-200 Mt. 28 75 Brief history and fundamental principles of photocatalytic materials for CO 2 reductionRenewable solar energy, harnessed via innovative catalysts and reactors, has the potential to photoreduce linear CO 2 molecules by breaking the C=O bonds to form C-H bonds and then to yield 80 Plastics Advances in nanomaterials synthesis offer new routes to solar fuels and chemicals from CO 2 as a sustainable chemical feedstock

The thermal decomposition of hydroxyl-terminated generation-4 polyamidoamine dendrimer (G4OH) films deposited on Au surfaces has been compared with decomposition of the same dendrimer encapsulating an approximately 40-atom Pt particle (Pt-G4OH). Infrared absorption reflection spectroscopy studies showed that, when the films were heated in air to various temperatures up to 275 degrees C, the disappearance of the amide vibrational modes occurred at lower temperature for the Pt-G4OH film. Dendrimer decomposition was also investigated by thermogravimetric analysis (TGA) in both air and argon atmospheres. For the G4OH dendrimer, complete decomposition was achieved in air at 500 degrees C, while decomposition of the Pt-G4OH dendrimer was completed at 400 degrees C, leaving only platinum metal behind. In a nonoxidizing argon atmosphere, a greater fraction of the G4OH decomposed below 300 degrees C, but all of the dendrimer fragments were not removed until heating above 550 degrees C. In contrast, Pt-G4OH decomposition in argon was similar to that in air, except that decomposition occurred at temperatures approximately 15 degrees C higher. Thermal decomposition of the dendrimer films on Au surfaces was also studied by temperature programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS) under ultrahigh vacuum conditions. Heating the G4OH films to 250 degrees C during the TPD experiment induced the desorption of large dendrimer fragments at 55, 72, 84, 97, 127, 146, and 261 amu. For the Pt-G4OH films, mass fragments above 98 amu were not observed at any temperature, but much greater intensities for H(2) desorption were detected compared to that of the G4OH film. XPS studies of the G4OH films demonstrated that significant bond breaking in the dendrimer did not occur until temperatures above 250 degrees C and heating to 450 degrees C caused dissociation of C=O, C-O, and C-N bonds. For the Pt-G4OH dendrimer films, carbon-oxygen and carbon-nitrogen bond scission was observed at room temperature, and further decomposition to atomic species occurred after heating to 450 degrees C. All of these results are consistent with the fact that the Pt particles inside the G4OH dendrimer catalyze thermal decomposition, allowing dendrimer decomposition to occur at lower temperatures. However, the Pt particles also catalyze bond scission within the dendrimer fragments so that decomposition of the dendrimer to gaseous hydrogen is the dominant reaction pathway compared to desorption of the larger dendrimer fragments observed in the absence of Pt particles.