Nanocarbon-Edge-Anchored High-Density Pt Atoms for 3-nitrostyrene Hydrogenation: Strong Metal-Carbon Interaction

摘要

class="head no_bottom_margin" id="sec1title">IntroductionSupported metal catalysts with metal particles finely dispersed on high-surface-area support materials are vital for many industrially important catalytic reactions. The surface physicochemical properties of the supports play a crucial role in modifying the catalytic behaviors of supported metal species via the strong metal-support interaction (SMSI) (, , ; , ). The classical SMSI phenomenon was discovered on titania-supported Pt-group metals of which high temperature reduction significantly influenced the adsorption properties of small molecules such as H2 and CO (). It has been reported that pretreatment and reaction conditions induce the SMSI as well in oxides supported Au (for CO oxidation) () and Rh (for CO2 reduction by H2) catalysts (), which are termed oxidative and adsorbate-mediated SMSI. Recent reports demonstrated that carbides (), phosphates (, ), and layered double hydroxides () supported Au catalysts exhibited the SMSI effects for water-gas shift, CO oxidation, and ethanol dehydrogenation reactions, respectively. The SMSI has been widely exploited to improve catalyst stability (, , ), identify reaction mechanisms (href="#bib36" rid="bib36" class=" bibr popnode">Matsubu et al., 2017, href="#bib6" rid="bib6" class=" bibr popnode">Bonanni et al., 2012), and enhance activity (href="#bib54" rid="bib54" class=" bibr popnode">Vannice, 1979, href="#bib47" rid="bib47" class=" bibr popnode">Sonstrom et al., 2011). It is highly desired to extend the applications of SMSI concept to broader catalyst systems, beyond metal particles, to tune catalytic properties for desirable performance.Carbon-based catalysts have been widely used in liquid phase hydrogenation reactions because of their high chemical stability, high total surface area, and unique electronic properties (href="#bib48" rid="bib48" class=" bibr popnode">Su et al., 2017). It has been reported that the interaction between metal species and carbon surfaces can be significantly strengthened by engineering defects of, introducing functional groups to, and/or incorporating heteroatoms in carbon structures (href="#bib8" rid="bib8" class=" bibr popnode">Charlier, 2002, href="#bib30" rid="bib30" class=" bibr popnode">Lordi et al., 2001, href="#bib17" rid="bib17" class=" bibr popnode">Ebbesen and Takada, 1995). For example, single metal atoms that are anchored onto heteroatom-doped (e.g., N, O) carbon materials exhibited excellent catalytic performance for various catalytic transformations, such as methane activation (href="#bib12" rid="bib12" class=" bibr popnode">Cui et al., 2018), selective hydrogenation (href="#bib61" rid="bib61" class=" bibr popnode">Yan et al., 2015), hydrogen evolution (href="#bib18" rid="bib18" class=" bibr popnode">Fei et al., 2015, href="#bib25" rid="bib25" class=" bibr popnode">Liu et al., 2018), and oxygen reduction (href="#bib64" rid="bib64" class=" bibr popnode">Zitolo et al., 2015, href="#bib24" rid="bib24" class=" bibr popnode">Li et al., 2018). The uniformity of isolated active sites and the strong interaction between individual metal atoms and support surfaces facilitate the tuning of both selectivity and activity (href="#bib43" rid="bib43" class=" bibr popnode">Qiao et al., 2011, href="#bib26" rid="bib26" class=" bibr popnode">Liu, 2017a, href="#bib27" rid="bib27" class=" bibr popnode">Liu, 2017b, href="#bib20" rid="bib20" class=" bibr popnode">Gates et al., 2017, href="#bib55" rid="bib55" class=" bibr popnode">Wang et al., 2018, href="#bib9" rid="bib9" class=" bibr popnode">Chen et al., 2018). However, the structure of high-surface-area activated carbon supports can become extremely complex and consequently poses formidable challenges for correlating the metal-carbon interaction with the observed catalytic properties.In this work, we fabricated hollow nanocarbons (h-NCs) that possess high-number density of surface edge/defect sites, high total surface area, and highly accessible mesopores. We anchored ∼1.0 wt.% single Pt atoms to the edge/defect sites of the h-NCs to synthesize h-NC supported Pt1 single-atom catalysts (SACs), denoted as 1.0 wt.% Pt1/h-NC. The selective hydrogenation of 3-nitrostyrene to functionalized anilines, which are industrially key intermediates for fine chemicals (href="#bib15" rid="bib15" class=" bibr popnode">Downing et al., 1997, href="#bib10" rid="bib10" class=" bibr popnode">Corma and Serna, 2006), was chosen to probe how the SMSI between carbon and single metal atoms affects the catalytic performance of the fabricated Pt1/h-NC SAC for liquid phase catalytic reactions. Our comprehensive characterization results indicate that the strong interaction between Pt atoms and carbon edge/defect sites modulates the electronic structure of the anchored single Pt atoms and thus their reactivity. The 1.0 wt.% Pt1/h-NC demonstrates excellent activity for hydrogenation of 3-nitrostyrene to 3-vinylaniline with a turnover number (TON) > 31,000/h, more than 20 times higher than that of the best catalyst for such selective hydrogenation reactions reported in the literature (href="#bib59" rid="bib59" class=" bibr popnode">Wei et al., 2014).