02344nas a2200169   4500008004100000022001400041245011700055210006900172260007100241300001600312490000800328520165200336100001701988700001602005700002602021856012702047       2013                        eng d  a1932-744700aInfluence of charge and ligand on the finite temperature behavior of gold clusters: a BOMD study on Au-6 cluster0 aInfluence of charge and ligand on the finite temperature behavio  a1155 16TH ST, NW, WASHINGTON, DC 20036 USAbAMER CHEMICAL SOCcOCT  a20982-209900 v1173 a<p>Conformation and electronic charge on a gold cluster are known to determine its catalytic property. However, little is known on the finite temperature behavior of various gold cluster conformations. Much less is known on the role of charge or a ligand in stabilizing a conformation at finite temperatures. In this work, we have carried out relativistic density functional theory (DFT) based molecular dynamical simulations on neutral and charged Au-6 clusters with an aim of understanding the stability of ground state conformations as a function of charge on the cluster. Our simulations reveal that cationic and anionic Au-6 clusters undergo conformational transitions at 500 K where as neutral Au-6 cluster retains its ground state conformation up to a temperature of 1100 K. In order to look into the factors leading to the stabilization of neutral Au-6 cluster (or destabilization of cationic and anionic Au-6 clusters), structural and electronic properties are analyzed. Factors such as charge redistribution within the atoms and composition of molecular orbitals are seen to contribute towards stronger Au-Au bonds in Au-6(0) thereby stabilizing it considerably. Following the analysis, simulations are also extended to neutral, cationic, and anionic Au-6-COn (n = 1,2) complexes. In the case of CO chemisorbed Au-6 clusters, neutral and negatively charged ground state conformations are stable up to nearly 800 K, while the positively charged Au-6 ground state conformation collapses at room temperature. This work, in short demonstrates how charge or even a ligand can be used to moderate the physical properties of a gold cluster.</p>1 aManzoor, Dar1 aPal, Sourav1 aKrishnamurty, Sailaja  uhttps://library.ncl.res.in/content/influence-charge-and-ligand-finite-temperature-behavior-gold-clusters-bomd-study-au-6-002006nas a2200169   4500008004100000022001400041245008700055210006900142260000900211300001400220490000800234520142600242100001701668700002601685700001601711856010901727       2014                        eng d  a1932-744700aEffect of silicon doping on the reactivity and catalytic activity of gold clusters0 aEffect of silicon doping on the reactivity and catalytic activit  cAPR   a7501-75070 v1183 a<p>Doping is known to be an excellent and simple way of catalyst design. Although notable progress has been made in understanding the reactivity and catalytic activity of gas-phase and supported gold clusters, very few studies have been carried out on the doped gold clusters. In the present work, we have carried out density functional theory calculations to investigate the effect of silicon doping on the reactivity and catalytic activity of gold nanoclusters. The present work particularly focuses on the adsorption and activation of molecular oxygen on the pristine and silicon-doped gold clusters. The results confirm that the silicon-doped Au7Si cluster shows considerable binding and activation of the O-2 molecule in comparison to the pristine Au-8 cluster as reflected in the relevant geometrical parameters (O-O and Au-O bond lengths) and O-O stretching frequency. However, silicon doping has no contrasting effect on the reactivity and catalytic activity of the Au-7 cluster. In addition to the stronger binding and activation of the O-2 molecule, the doped Au7Si cluster leads to a significant reduction in the activation barrier (0.57 eV) for the environmentally important CO oxidation reaction in contrast to the catalytically inactive pristine Au-8 cluster (1.22 eV). Thus, our results highlight the critical role of doping foreign impurities for future endeavors in the field of gold nanocatalysis.</p>
1 aManzoor, Dar1 aKrishnamurty, Sailaja1 aPal, Sourav  uhttps://library.ncl.res.in/content/effect-silicon-doping-reactivity-and-catalytic-activity-gold-clusters01803nas a2200229   4500008004100000022001400041245009900055210006900154260011000223300001300333490000700346520091800353653002501271653003601296653001801332653001901350653002001369653002601389100001701415700001601432856012501448       2014                        eng d  a0376-471000aEnhanced interaction of molecular oxygen with amino acid complexes of silver and gold clusters0 aEnhanced interaction of molecular oxygen with amino acid complex  aDR K S KRISHNAN MARG, PUSA CAMPUS, NEW DELHI 110 012, INDIAbNATL INST SCIENCE COMMUNICATION-NISCAIRcAUG  a996-10000 v533 a<p>Density functional theory calculations have been carried out to study the effect of amino acid adsorption on the reactivity of silver and gold clusters with molecular oxygen. It is found that the amino acids glycine and alanine form stable complexes with both Ag-4 and Au-4 clusters. However, the extent of interaction is more in the case of the Au-4 cluster, as reflected from the increase in binding energy in the amino acid Au-4 complexes. Our results confirm that the adsorption of amino acids glycine and alanine enhances the reactivity of Ag-4 and Au-4 clusters towards O-2 molecule. The enhanced reactivity of O-2 molecule towards the amino acid metal cluster complexes is manifested by an increase in the O-2 binding energy and a decrease in the M-O (M = Ag, Au) bond length. Moreover, it is found that the co-adsorption of amino acids and O-2 molecule on the Ag-4 and Au-4 clusters is cooperative.</p>10aAmino acid complexes10aDensity functional calculations10aGold clusters10aMetal clusters10aSilver clusters10aTheoretical chemistry1 aManzoor, Dar1 aPal, Sourav  uhttps://library.ncl.res.in/content/enhanced-interaction-molecular-oxygen-amino-acid-complexes-silver-and-gold-clusters-001933nas a2200157   4500008004100000022001400041245011000055210006900165260007100234300001600305490000800321520128500329100001701614700001601631856012801647       2014                        eng d  a1932-744700aHydrogen atom chemisorbed gold clusters as highly active catalysts for oxygen activation and co oxidation0 aHydrogen atom chemisorbed gold clusters as highly active catalys  a1155 16TH ST, NW, WASHINGTON, DC 20036 USAbAMER CHEMICAL SOCcDEC  a30057-300620 v1183 a<p>Using oxygen activation and carbon monoxide oxidation as a probe, we have carried out density functional theory (DFT) calculations to investigate the effect of hydrogen atom chemisorption on the reactivity and catalytic activity of gold nanoclusters. In the present work, we particularly focus on the closed shell neutral Au-n (n = 2, 4, 6, 8) gold clusters which are reported to be chemically inert and catalytically less active. The results confirm that the hydrogen atom chemisorption activates the inert clusters, thereby leading to enhanced binding and activation of the O-2 molecule. A significant amount of increase in the O-O and decrease in the Au-O bond lengths together with a pertinent red shift in the O-O stretching frequencies clearly indicates the stronger binding and activation of oxygen molecule in the case of AunH clusters. Further, our results reveal that the hydrogen atom chemisorbed gold clusters are catalytically more active with low activation barriers for the CO oxidation reaction compared to the parent less active closed shell gold clusters. Thus, in short the current theoretical observation provides key inputs for enhancing the reactivity and catalytic activity of inert gold clusters through the adsorption of a small atom or a molecule.</p>1 aManzoor, Dar1 aPal, Sourav  uhttps://library.ncl.res.in/content/hydrogen-atom-chemisorbed-gold-clusters-highly-active-catalysts-oxygen-activation-and-co02235nas a2200157   4500008004100000022001400041245008300055210006900138260007100207300001400278490000800292520162700300100001701927700001601944856011701960       2015                        eng d  a1089-563900aReactivity and catalytic activity of hydrogen atom chemisorbed silver clusters0 aReactivity and catalytic activity of hydrogen atom chemisorbed s  a1155 16TH ST, NW, WASHINGTON, DC 20036 USAbAMER CHEMICAL SOCcJUN  a6162-61700 v1193 a<p>Metal clusters of silver have attracted recent interest of researchers as a result of their potential in different,catalytic applications and low Cost. However, due to the completely filled d orbital and very high first ionization potential of the silver atom, the silver-based catalysts interact very weakly with the reacting molecules. In the current work, density functional theory calculations were carried out to investigate the effect of hydrogen atom chemisorption. On the reactivity and catalytic properties of inert silver clusters Our results affirm that the hydrogen atom chemisorption leads to enhancement the binding energy of the adsorbed O-2 molecule on the inert silver clusters. The increase in the binding energy is also characterized by the decrease in the Ag-O and increase in the O-O bond lengths in the case of the AgnH Silver clusters. Pertinent to the increase in the O-O bond length, a. significant red shift in the O-O Stretching frequency is. also noted in the case,of the AgnH silver clusters. Moreover, the hydrogen atom chemisorbed silver clusters show low reaction barriers and heat Of formation of the final products for the,environmentally important CO oxidation reaction as compared to the parent catalytically inactive clusters The obtained results were compared with those of the corresponding gold and hydrogen atom chemisorbed gold clusters obtained at the same level of theory. It is expected the current computational study will provide key insights for future advances in the design of efficient nanosilver-based catalysts through the adsorption of a small atom or a ligand.</p>1 aManzoor, Dar1 aPal, Sourav  uhttps://library.ncl.res.in/content/reactivity-and-catalytic-activity-hydrogen-atom-chemisorbed-silver-clusters-001930nas a2200157   4500008004100000245016500041210006900206260000800275300001600283490000800299520127400307100001701581700002601598700001601624856013201640       2016                        eng d00aContriving a catalytically active structure from an inert conformation: a density functionalinvestigation of Al, Hf, and Ge doping of Au-20 tetrahedral clusters0 aContriving a catalytically active structure from an inert confor  cSEP  a19636-196410 v1203 a<p>The transformation of an inert structure into a catalytically active conformation has immense potential from a structural engineering point of view. In the present work, we explored methods of achieving such a transformation through a density-functional-based study. Au-20 is known be one of the most stable and catalytically inert gold clusters, with a well-known tetrahedral structure. We demonstrate the transformation of the inert Au-20 conformation into a highly active catalytic cluster through selective doping with Hf and Ge atoms. Depending on the dopant, the inert tetrahedral Au-20 cluster evolves into either an endohedral or a hollow-cage-like conformation. The structural changes are manifested in the catalytic properties as well, with the result that the transformed doped cages exhibit extremely low activation barriers for the environmentally important CO oxidation reaction as compared to reported inert Au-20 cluster. The activation barriers for CO oxidation are particularly low (&lt;0.12 eV) when germanium is directly involved in the CO oxidation. Thus, the current work highlights the importance of engineering structural properties of metal nanoclusters with the help of heteroatom dopants for future applications in efficient catalysis.</p>1 aManzoor, Dar1 aKrishnamurty, Sailaja1 aPal, Sourav  uhttps://library.ncl.res.in/content/contriving-catalytically-active-structure-inert-conformation-density-functionalinvestigation02379nas a2200169   4500008004100000022001400041245009500055210006900150260011000219300001400329490000700343520167300350100001702023700002602040700001602066856012702082       2016                        eng d  a1463-907600aEndohedrally doped gold nanocages: efficient catalysts for O-2 activation and CO oxidation0 aEndohedrally doped gold nanocages efficient catalysts for O2 act  aTHOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLANDbROYAL SOC CHEMISTRYcMAR  a7068-70740 v183 a<p>Gold nanocages are the most attractive catalytic materials as all the atoms in the cage type clusters reside on the surface, making them available for chemisorption by reacting molecules. Due to a hollow space at the center, their chemical and catalytic properties can be tuned effectively and easily by endohedral doping. While a significant experimental and theoretical understanding is currently available on the structural and electronic properties of doped gold cages, very little information is available on their reactivity and catalytic behavior. In the present work, with the help of density functional theory calculations we demonstrate that endohedral doping leads to a notable increase in the binding energy of molecular oxygen on the gold nanocages. The enhancement in the O-2 binding energy on the doped gold cages is also confirmed by a significant decrease in the Au-O and an increase in the O-O bond lengths, corroborated by a red shift (similar to 250 cm(-1)) in the O-O stretching frequency as compared to the pristine cage. Furthermore, interestingly, the doped gold cages show very low activation barriers for the environmentally important CO oxidation reaction as compared to the pristine gold cage. Importantly, the decrease in the barrier height is comparatively greater for the rate limiting step of O-O-C-O intermediate formation and as a result the CO oxidation is expected to be more facile on the doped gold cages. Thus, the current study highlights the role of heteroatom doping in imparting new chemical and catalytic properties to gold cages and is expected to spur further research in the design of efficient gold nanocatalysts.</p>1 aManzoor, Dar1 aKrishnamurty, Sailaja1 aPal, Sourav  uhttps://library.ncl.res.in/content/endohedrally-doped-gold-nanocages-efficient-catalysts-o-2-activation-and-co-oxidation-0