Multimetallic (de)hydrogenation catalysed processes

The use of different metals working together in a synergistic way, allows synthetic transformations that are not achievable by other means. The metal cooperation becomes important in catalytic processes for the synthesis of sophisticated molecules or difficult transformations. A rationale design of multimetallic catalysed processes entails metal complexes and reaction conditions being compatible, which in general is not straightforward. A key feature for success found in all systems dealing with multimetallic processes is catalyst stability. The use of robust metal complexes increases the probability of success in the search of tandem catalytic processes. This microreview is based on the recent and most important findings of multimetallic catalysed processes that involved (de)hydrogenation reactions. The field constitutes a research area that is full of potential and can be foreseen that relevant applications will be described in the near future.MINECO (CTQ2015-69153-C2-2-R), Generalitat Valenciana (AICO/2015/039), Universitat Jaume I (P1.1B2015-09

Enhancement of gold catalytic activity and stability by immobilization on the surface of graphene

The catalytic performance of gold complexes is evaluated at the molecular level and when supported onto reduced graphene oxide (rGO). Gold complexes of general formula [(NHC)AuX] catalyse the synthesis of indoles via intramolecular hydroamination reaction of alkynes. The catalytic properties of the molecular gold complexes are highly improved when supported onto graphene. Faster reaction rates and higher catalyst stability are observed for the immobilized gold complexes. The use of graphene as support of molecular complexes has a positive benefit in the catalytic gold properties in terms of activity and stabilityThe authors thank the financial support from MINECO (CTQ2015-69153-C2-2-R), Generalitat Valenciana (AICO/2015/039) and Universitat Jaume I (P1.1B2015-09). D. V-E thanks MINECO for a FPU grant (FPU15/03011

Ruthenium molecular complexes immobilized on graphene as active catalysts for the synthesis of carboxylic acids from alcohol dehydrogenation

Ruthenium complexes containing N-heterocyclic carbene ligands functionalized with different polyaromatic groups (pentafluorophenyl, anthracene, and pyrene) are immobilized onto the surface of reduced graphene oxide. The hybrid materials composed of organometallic complexes and graphene are obtained in a single-step process. The hybrid materials are efficient catalysts for the synthesis of carboxylic acids from the dehydrogenation of alcohols in aqueous media. The catalytic materials can be recycled up to ten times without significant loss of activity. The catalytic activity of the pyrene derivative, Pyr-Ru (3) is enhanced when the ruthenium complex is anchored onto the surface of graphene. The carbonaceous material limits the degradation of the ruthenium complex resulting in increased activity and requiring lower catalyst loadings. The catalytic process of the pyrene hybrid material is heterogeneous in nature due to the strong interaction between the pyrene and graphene. The catalytic process of the anthracene and pentafluorophenyl hybrid materials is governed by the so-called ‘boomerang effect’. The ruthenium molecular complex is released from and returned to the graphene surface during the catalytic reaction. Mechanistic insight has been obtained experimentally and theoretically. The energy profile suggests that the rate-determining step is the water nucleophilic attack to a coordinated aldehyde complex to form a gem-diolate complex.The authors thank the financial support from MINECO (CTQ2015-69153-C2-2-R and CTQ2015- 67461-P), Generalitat Valenciana (AICO/2015/039), Universitat Jaume I (P1.1B2015-09) and Universidad de Zaragoza (UZ2014-CIE-01)

Catalytic Dehydrogenative Coupling of Hydrosilanes with Alcohols for the Production of Hydrogen On-demand: Application of a Silane/Alcohol Pair as a Liquid Organic Hydrogen Carrier

The compound [Ru(p-cym)(Cl)2(NHC)] is an effective catalyst for the room-temperature coupling of silanes and alcohols with the concomitant formation of molecular hydrogen. High catalyst activity is observed for a variety of substrates affording quantitative yields in minutes at room temperature and with a catalyst loading as low as 0.1 mol %. The coupling reaction is thermodynamically and, in the presence of a Ru complex, kinetically favourable and allows rapid molecular hydrogen generation on-demand at room temperature, under air, and without any additive. The pair silane/alcohol is a potential liquid organic hydrogen carrier (LOHC) for energy storage over long periods in a safe and secure way. Silanes and alcohols are non-toxic compounds and do not require special handling precautions such as high pressure or an inert atmosphere. These properties enhance the practical applications of the pair silane/alcohol as a good LOHC in the automotive industry. The variety and availability of silanes and alcohols permits a pair combination that fulfils the requirements for developing an efficient LOHC

A No-Lose Theorem for Higgs Searches at a Future Linear Collider

Assuming perturbativity up to a high energy scale $\sim 10^{16}$ GeV, we demonstrate that a future $e^+e^-$ linear collider operating at $\sqrt{s} =$ 500 GeV with $\int{\cal L}=$ 500 fb$^{-1}$ per year (such as the recently proposed TESLA facility) will detect a Higgs boson signal regardless of the complexity of the Higgs sector and of how the Higgs bosons decay.Comment: 4 pages, LaTe

Reduced Graphene Oxides as Carbocatalysts in Acceptorless Dehydrogenation of N-Heterocycles

[EN] The catalytic properties of graphene-derived materials are evaluated in acceptorless dehydrogenation of N-heterocycles. Among them, reduced graphene oxides (rGOs) are active (quantitative yields in 23 h) under mild conditions (130 degrees C) and act as efficient heterogeneous carbocatalysts. rGO exhibits reusability and stability at least during eight consecutive runs. Mechanistic investigations supported by experimental evidence (i.e., organic molecules as model compounds, purposely addition of metal impurities and selective functional group masking experiments) suggest a preferential contribution of ketone carbonyl groups as active sites for this transformation.Supported by MCIN/AEI/10.13039/501100011033/FEDER (Grant Nos. RTI2018-098237-B-C21, RTI2018-098237-BC22, and PID2019-105881RB-I00), Generalitat Valenciana (No. PROMETEU/2020/028), and Universitat Jaume I (No. UJI-B2018-23).Mollar-Cuni, A.; Ventura-Espinosa, D.; Martin, S.; García Gómez, H.; Mata, JA. (2021). Reduced Graphene Oxides as Carbocatalysts in Acceptorless Dehydrogenation of N-Heterocycles. ACS Catalysis. 11(23):1-6. https://doi.org/10.1021/acscatal.1c04649S16112

Stabilization of Nanoparticles Produced by Hydrogenation of Palladium–N-Heterocyclic Carbene Complexes on the Surface of Graphene and Implications in Catalysis

Palladium nanoparticles (NPs) have been obtained by decomposition of well-defined palladium complexes noncovalently anchored onto the surface of reduced graphene oxide. Morphological analysis by microscopy showed the presence of small palladium NPs homogeneously distributed on the support. Characterization by X-ray photoelectron spectroscopy confirmed that palladium NPs contain Pd(2+) and Pd(0) oxidation states and the presence of N-heterocyclic carbene and bromo ligands. The catalytic properties of the NPs with and without the support have been evaluated in the hydrogenation of alkynes. Supported palladium NPs showed increased activity versus the nonsupported ones and could be recycled up to 10 times without the loss of catalytic activity. The composition of the palladium NPs is different for each catalytic cycle indicating a dynamic process and the formation of different catalytic active species. On the contrary, the unsupported palladium NPs showed limited activity caused by decomposition and could not be recycled. The role of the support has been investigated. The results indicate that the support influences the stability of palladium NPs

In situ decoration of graphene sheets with gold nanoparticles synthetized by pulsed laser ablation in liquids

The demand for nanocomposites of graphene and carbonaceous materials decorated with metallic nanoparticles is increasing on account of their applications in science and technology. Traditionally, the production of graphene-metal assemblies is achieved by the non-environmentally friendly reduction of metallic salts in carbonaceous suspensions. However, precursor residues during nanoparticle growth may reduce their surface activity and promote cross-chemical undesired effects. In this work we present a laser-based alternative to synthesize ligand-free gold nanoparticles that are anchored onto the graphene surface in a single reaction step. Laser radiation is used to generate highly pure nanoparticles from a gold disk surrounded by a graphene oxide suspension. The produced gold nanoparticles are directly immobilized onto the graphene surface. Moreover, the presence of graphene oxide influences the size of the nanoparticles and its interaction with the laser, causes only a slight reduction of the material. This work constitutes a green alternative synthesis of graphene-metal assemblies and a practical methodology that may inspire future developments.The authors thank the financial support from Generalitat Valenciana through the programs PROMETEO-2012-021, AICO/2016/036 and AICO/2015/039, a fellowship (S. Sabater) and a research contract (D. Ventura-Espinosa), the University Jaume I through the projects P1·1B2013-53 and P1.1B2015-09, and the Ministerio de Economía y Competitividad (MINECO) through the projects FIS2013-40666-P and CTQ2015-69153-C2-2-R. The authors are also very grateful to the ‘Serveis Centrals d’Instrumentació Científica (SCIC)’ of the University Jaume I for the use of the femtosecond laser and microscopy facilities. We thank S. Solans for his help with XPS analysis and interpretation. R. Torres-Mendieta gratefully acknowledges the Generalitat Valenciana support for a Santiago Grisolia scholarship GRISOLIA/2013/015

Influence of nanoparticle morphology and its dispersion ability regarding thermal properties of water used as phase change material

Nanoparticles with different morphologies were added to water to study if the morphology of the nanoparticles affects the main parameters of water used as phase change material (PCM). Considered morphologies were spherical, tubes and sheets in the form of spherical carbon black nanoparticles (CB), multiwalled carbon nanotubes (MWCNT), and graphene oxide nanosheets (GO). Results demonstrate that effectively the morphology of nanoparticles affect the thermophysical properties of the nano-enhanced PCM (NePCM). Depending on the morphology of the added nanoparticle, the final NePCM will have different subcooling and thermal conductivity, whereas its phase change enthalpy is not affected and, therefore, is the same for all produced NePCM

Improving Catalyst Activity in Hydrocarbon Functionalization by Remote Pyrene–Graphene Stacking

A copper complex bearing an N‐heterocyclic carbene ligand with a pyrene “tail” attached to the backbone has been prepared and supported on reduced graphene oxide (rGO). The free and supported copper materials have been employed as homogeneous and heterogeneous catalysts in the functionalization of hydrocarbons such as n‐hexane, cyclohexane, and benzene through incorporation of the CHCO2Et unit from ethyl diazoacetate. The graphene‐anchored complex displays higher reaction rates and induces higher yields than its soluble counterpart, features that can be rationalized in terms of a decrease in electron density at the metal center due to a remote net electronic flux from the supported copper complex to the graphene surface.The authors would like to thank the financial support of the MINECO (CTQ2017-82893-C2-1-R and CTQ2015-69153-C2-2- R), Junta de Andalucía (P12-FQM-1765) and Universitat Jaume I (UJI-B2018-23). D. V-E thanks the MINECO for a grant (FPU15/03011). The authors thank the ‘Servei Central d’Instrumentació Científica (SCIC)’ of the Universitat Jaume I