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The fundamental understanding of the electronic and geometric structures of small platinum clusters on metal oxide support is important to design the futuristic Pt-based novel materials for heterogeneous catalysis. Here we report a systematic theoretical study on the trend in the structural and electronic properties of alumina supported Pt n (n = 1–7 and 10) clusters with a focus to highlight the effect on the substrate. All calculations were carried out using the plane wave based pseudo-potential approach. The model for the support has been designed by using Al-terminated α-Al 2 O 3 (0001) surface which is the most stable surface termination under ultrahigh vacuum conditions. The results show that the binding of Pt atom with the Al 2 O 3 surface releases 1.84 eV energy which is significantly higher than atomic adsorption energy of other noble metal atoms (Ag, Au, and Pd). As a consequence, the equilibrium geometries of free Pt n clusters (n = 3–7) are significantly altered on the alumina surface. Whilst Pt 10 cluster favors tetracapped prism structure in the gas phase, on alumina support it prefers a layered structure. The geometrical changes of Pt clusters on the alumina surface have been attributed to the energy balance between the Pt-Pt and Pt-substrate interactions. The nature of interaction between the Pt n clusters and surface has been verified using the electronic density of states analysis. Surface induced electronic charge on the deposited cluster results in red shift in its energy levels, indicating electron rich activation of platinum clusters. The inclusion of spin-orbit coupling(SOC) significantly changes the electronic structure of gas phase platinum cluster; however, the extent of SOC influence reduces due to interfacial bonding with alumina support. [ABSTRACT FROM AUTHOR]

Here we report the adsorption and decomposition behavior of dimethyl methyl-phosphonate (DMMP) on pristine and defected graphene using the first principles theory. The primary objective of this study is to highlight the importance of a vacancy defect on the adsorption mechanism of a molecule. In order to account for the weak forces involved between the molecule and graphene, we have used dispersion corrected total energy calculations along with generalized gradient approximation scheme for the exchange correlation energy. Among various possible configurations, the most stable geometry shows oxygen atom of the DMMP molecule favors to be close to the surface plane and bind with one of the unsaturated carbon atoms at the defect site. The molecule-substrate interaction energy is stronger for defected graphene than pristine graphene. The decomposition of the DMMP molecule at the vacancy site of the defected graphene has been investigated. For the dissociative adsorption, it is seen that the C H bond of the DMMP breaks and H atom is transferred to one of the low-coordinated C-atoms at the vicinity of the defect, forming new C H bond. In addition, the C C bond formation between graphene and DMMP occurs. Finally, the nature of bonding and electronic structure at the interface was interpreted through site projected electronic density of states analysis. [ABSTRACT FROM AUTHOR]

The understanding of atomic adsorption on a solid surface is essential to understand the fundamental issue of chemical interaction at the hetero-junctions, formed by two metals. With an aim to compare the adsorption behavior between finite size cluster and extended surface, M atom (M = Ni, Pd, Pt) interaction with Ag n /Au n ( n = 3, 6) clusters and periodic slab of Ag(111)/Au(111) surfaces is investigated theoretically. All calculations are performed using plane-wave pseudo-potential approach under the spin-polarized density functional theory including the spin–orbit coupling term. The results show that the interaction of M atom with small clusters is primarily governed by the relative strength of M Ag/Au vs. Ag Ag/Au Au bonds. The stronger interaction follows rearrangement of the host cluster. For the periodic slab, M atom prefers to adsorb on the fcc site with small local distortion. Due to variation in the strength of interaction and amount of distortion, the cluster and periodic slab differs in absolute adsorption energy values. Further a comparative analysis of chemical bonding through electronic density of state (EDOS) and orbital decomposed charge distribution infers that interaction of Ni/Pd/Pt with gold substrate is stronger than silver substrate. [ABSTRACT FROM AUTHOR]

Abstract: In this work, based on first principles density functional theory, we have investigated the interaction of SO3 molecule on three different substrates; (i) clean Al2O3 surface (0001) (ii) an isolated Ag6 cluster and (iii) Ag6 clusters deposited on the Al2O3 surface. All calculations were carried out using the plane wave based pseudopotential method under the framework of density functional theory. For the clean Al2O3 surface, the SO3 molecule was adsorbed in parallel orientation on the surface resulting in an elongation of the S–O bond from 1.44 to 1.52 Å with interaction energy of 1.67 eV. In contrast, the interaction of SO3 with Ag6 was found to be weak with 0.4 eV interaction energy and 1.47 Å as the largest S–O bond length. Remarkably, when SO3 molecule interacted with Ag6 cluster deposited on the Al2O3 support, the binding was found to be higher than both Al2O3 and Ag6 clusters in their isolated state. In particular, upon adsorption of SO3 on Ag6/@Al2O3, the S–O bond length was found to increases from 1.44 to 1.64 Å and the interaction energy was estimated to be 2.00 eV. As the bond elongation bears the signature of bond weakening, a comparison of the above three results clearly suggests that the dissociation barrier of S–O bond on the Ag6@Al2O3 support will be significantly lower than that on the isolated Ag6 or Al2O3 surface. The nature of chemical interaction of SO3 on these three systems has been discussed based on the electronic density of states analysis. [Copyright &y& Elsevier]

[Display omitted] • Comparative DFT study of the electronic and geometrical properties of alumina supported M 10 (M = Ag, Au, Pd, and Pt) clusters. • Finite size M 10 @Al 2 O 3 cluster's chemical reactivity for molecular oxygen activation and dissociation have been equated with crystalline 111 facets of bulk counterpart. • Ag 10 @Al 2 O 3 , Au 10 @Al 2 O 3 and Pd 10 @Al 2 O 3 show increase in inter-metallic bond lengths and move away from substrate during oxidation, whilst, Pt 10 @Al 2 O 3 display robust behaviour by moving near to surface. A comprehensive study of electronic and geometrical properties of alumina supported M 10 (M = Ag, Au, Pd, Pt) clusters has been reported with a focus to unravel chemical reactivity towards oxidative catalysis. Au 10 , Ag 10 and Pd 10 clusters on alumina surface, adopt zigzag style hexagonal pseudo-planar structure aligning to substrate template, contrary Pt 10 @Al 2 O 3 does not follow surface template and forms a bilayer structure due to higher Pt Pt bond strength. Pd 10 and Pt 10 cluster bind with alumina surface stronger than Ag 10 and Au 10 and accordingly receives more charge from surface. The d -band centre of finite size M 10 @Al 2 O 3 cluster follows the trends of extended M(1 1 1) surface and Pt 10 @Al 2 O 3 shows close matching for d -band centre position values with Pt(1 1 1). On interaction with O 2 molecule, all four M 10 @Al 2 O 3 clusters energetically prefer surface assisted molecular adsorption (O 2 bridging cluster-surface) over atop molecular adsorption demonstrating pivotal role of substrate. In contrast, dissociative adsorption prefers atop mode configurations. During oxidation, whilst Ag 10 @Al 2 O 3 , Au 10 @Al 2 O 3 and Pd 10 @Al 2 O 3 show increase in M M bond-lengths and move away from substrate, Pt 10 @Al 2 O 3 displays robust behaviour by moving near to surface. Due to minimum overlap between 4d and 5s state (large difference in energy) the O 2 interaction energetics of Ag 10 @Al 2 O 3 as well as Ag(1 1 1) depart from usual d -band model. [ABSTRACT FROM AUTHOR]

• A model single atom catalyst where Au atom is embedded on the hexagonal boron nitride sheet is reported. • Effect of vacancy defects and Ni(111) support has been established. • Both boron and nitrogen vacancies stabilize the Au adatom on the h-BN. • The Au atom becomes electron deficient/rich depending upon the defect site. • Defected h-BN sheets are more stable on the Ni(111) support. • Au atom on VB/Ni is thermodynamically stable and acts as a good catalyst. In the present paper we report a model single atom catalyst where Au atom is on the hexagonal boron nitride (h-BN) sheet. The primary objective of this study is to compare the chemical reactivity of an Au atom embedded on freestanding h-BN monolayer (with and without vacancy defect) and the effect of Ni(111) support. We have used the plane wave based pseudo-potential approach under density functional theory for optimization of the geometries and electronic structure of all the systems. From the energetic criteria it is seen that the creation of boron vacancy is easier than nitrogen vacancy. However, the Au atom becomes electron deficient/rich depending on the defect site. It is seen that the defected h-BN sheets are more stable on the Ni(111) support than its pristine counterpart. Further to explore the catalytic proficiency of these systems interaction of molecular oxygen was studied on the Au embedded h-BN sheet (with and without defects) and deposited on the Ni(111) support. In our view these results are remarkable and therefore would expect to stimulate experimental verification. [ABSTRACT FROM AUTHOR]

• Small Sn n (n = 1–6, 10) cluster anchored on catalytically relevant MgO(1 0 0) substrate. • Sn-Sn interaction is found to be stronger than Sn n -MgO interaction and this helps in retaining the gas phase motif during interaction. • In contrast to gold cluster which previously have been known for pulling charge from MgO, tin clusters provides electronic charge to surface, • Sn cluster reciprocate relatively higher reconstruction and reordering of charge on MgO Surface. • Charge reordering on the MgO (1 0 0) surface after deposition of Sn 6 cluster. • Polarity variance along the MgO surface endorses its implication in heterogeneous catalysis. Catalysis with cluster-substrate complex materials has relevance for fundamental understanding and technological applications. Present work reports a systematic DFT study on Sn n (n = 1–6, 10) cluster adsorbed on catalytically relevant MgO(1 0 0) substrate. Results reveal that Sn-Sn interaction is stronger than Sn n -MgO interaction which helps in retaining gas phase motif during interaction. While smaller size tin clusters maximizes interaction with perfect MgO(1 0 0) surface through parallel orientation (more number of bond with surface atoms), larger cluster anchors on surface by single Sn-O bond only. Adsorption form of Sn cluster on perfect MgO surface are different from those reported in literature for gold cluster. Whilst gold cluster has been known for pulling charge from MgO, tin clusters provides electronic charge to MgO surface. Sn cluster reciprocate relatively higher reconstruction in MgO substrate due to charge transfer from adsorbate to substrate. This lead to significant reordering of electronic charge in MgO surface and induces variance in charge polarity across slab. Variance of charge polarity was reaffirmed by different adsorption behavior of water molecule across slab. Since ionic liquids has huge implications in catalyzing a solution phase reaction due to their polarity effect, likewise observed polarity variance along MgO surface endorses its implication in heterogeneous catalysis. [ABSTRACT FROM AUTHOR]

We report the H I bond activation on free and confined silver tetramer clusters using the first principles approach. The objective of this study is to underscore the effect of confinement on the chemical reactivity of Ag 4 . All calculations were carried out under the density functional theory formalism using both atomic and plane wave basis sets. We have used armchair carbon nanotube as a model system for confinement. The results show that the interaction energy is increased inside nanotube, leading to enhanced bond stretching. The origin of such effect has been demonstrated using molecular orbital theory and electronic density of state analysis. [ABSTRACT FROM AUTHOR]

Atomic level heterogenous catalysis has been of importance for in-depth understanding and designing of novel catalytic material. Present work aims to investigate the chemical reactivity of Au, Au 2 and Au 8 cluster on hexagonal boron nitride nano sheet (h-BN) and its Ni(111) activated analogue using density functional theory (DFT). The average vertical separation of gold atom(s) from h-BN is significantly influenced by Ni(111) support. Oxygen molecule, which is the key reactant for any oxidation reaction, is considered as probe molecule to verify the reactivity. Contrary to the case of Au atom, which is the most reactive on free-standing h-BN, Au 2 and Au 8 clusters show higher reactivity on Ni supported h-BN. Thus the agglomeration of Au (Au–Au interaction) and Ni(111) support is important in controlling the reactivity and therefore, will play a key role to design Au based efficient catalyst for future. [Display omitted] • On free-standing h-BNNS, Au atom and Au dimer favours on top B and N atoms, respectively. • With Ni (111) supported h-BNNS both Au and Au 2 favour on-top B atom. • On free-standing h-BNNS, Au elongates the O–O bond more than Au 2 and Au 8. • On Ni (111) supported h-BNNS, the O–O bond elongation is maximum on Au 8 cluster. • The presence of Ni(111) support improves the catalytic activity by spin modulation of the B atoms of h-BNNS. [ABSTRACT FROM AUTHOR]

Abstract: In the present study we report the hydrogen adsorption behavior of two SiC nanostructures; a planar sheet and a nanotube (10, 0) of 1 nm diameter decorated by Ti atoms on it. All calculations have been performed using a plane-wave based pseudopotential method. The lowest energy structure of the Ti adsorbed SiC sheet shows that Ti atom distorts the sheet in such a way that one of the Si atoms goes down the plane and the Ti atom bind with nearest three C atoms. The interaction of this Ti decorated sheet with hydrogen suggests that each Ti atom can bind up to four hydrogen molecules (all hydrogens are adsorbed in the molecular form) with an average binding energy of 0.37 eV. For SiC nanotube, the adsorption of Ti favors the hexagonal hollow site. Moreover, on interaction of this Ti decorated tube with hydrogen leads to dissociation of the first hydrogen molecule in the atomic form and thereafter adsorbs hydrogen in the molecular form. The average binding energy of hydrogen molecules on this Ti decorated tube is estimated to be 0.65 eV. Based on these results we infer that the Ti decorated SiC nanostructures moderately bind with hydrogen molecules (within the energy window for hydrogen storage materials) and therefore, can be considered as one of the potential hydrogen storage material. [Copyright &y& Elsevier]

Modification in optical responses of plasmonic metal nanoparticles by galvanic replacement reactions with metal ion contaminants has underpinned the development of Localised Surface Plasmon Resonance (LSPR) based sensors during past decade. However, the studies reported so far mostly use nanoparticles in the form of colloidal solution with inadequate understanding on the sensing mechanisms. We herein revisit the galvanic reaction between silver nanoparticles and Hg2+ ions with aims to develop a cellulose based optical test strip for selective assay of Hg2+ ions in aqueous samples as well as to comprehend the mechanisms of LSPR modification of AgNPs in interaction with Hg. The contact of cellulose membrane hosted AgNPs with Hg2+ ions follows classical galvanic reaction and a linear correlation between the measured absorbance of AgNPs with Hg2+ concentration has been found, which formed the basis of the quantitative assay. The performance of the sensor test strip has been verified for three real water samples of environmental and domestic origin. The results obtained are within 1–6 % accuracy with 94–106 % recovery. The detection limit of the present test strip has been found to be 0.3 ppb, which is lower than a large number of Hg2+ sensor developed so far. Using combined small angle X-ray scattering, calculated extinction coefficient and electronic structure calculations of Ag-Hg system by density functional theory computations, it has been demonstrated that at lower mercury concentration (below 1 ppm), the AgNPs undergo coalescence to form bigger nanoparticles. However at higher concentration (1 ppm and above), the Hg atoms undergo an exceptional "coat to droplet" conversion on AgNP surface. The associated changes in LSPR of AgNPs have been explained using these models. [ABSTRACT FROM AUTHOR]