Surface Molecule Manipulated Pt/TiO₂ Catalysts for Selective Hydrogenation of Cinnamaldehyde

Abstract

Surface states-the electronic states arising as a result of the different bonding environment-are easily contaminated by adsorbed molecules at nanoscale interfaces of metal nanoparticles (NPs), which generally poison the active sites of heterogeneous catalysts. Herein, we use selective hydrogenation of cinnamaldehyde (CAL) on platinum-covered titanium oxide (Pt@P25) as a prototype reaction, and show that the competitive exchange of extra-introduced species (sodium hydroxide and sodium formate) with spontaneously formed weak bound carbonate and bicarbonate anions at Pt NPs can reconstruct the surface states, which directs the preferred adsorption of the conjugated C=O and C=C double bonds of CAL, and consequently, results in highly efficient synthesis of unsaturated alcohol cinnamyl alcohol (COL) and saturated aldehyde hydrocinnamaldehyde (HCAL) with high selectivity of 94.7% and 97.6%, respectively. Our concept of restructured surface states to tune the chemoselectivity of α, β-unsaturated aldehydes triggered by the selective adsorption of alien molecules may lead to new design principles of heterogeneous catalysts, beyond the conventional d-band theory.

Physical Origin of Dual-Emission of Au–Ag Bimetallic Nanoclusters

“…Very recently, after long-term and systematic investigation, using a combined experimental and computational approach, in particular with the help of steady and ultra-fast absorption and emission spectra, we unambiguously confirmed the existence of new interface states due to the spatial overlapping of p orbitals of oxygen atoms of structural water molecules (SWs) at the confined nanointerface of soft and hard nanocavity (Hu et al, 2020;Yang et al, 2020b;Yang et al, 2019a;Chen et al, 2014;Yang et al, 2017;Yang et al, 2019b;Yang et al, 2019c;Hu et al, 2021;Shan et al, 2021;Tao et al, 2021).It is called the p band intermediate state (PBIS) with π bonding features, and not only provides an ensemble of intermediate states for bright photoluminescence (PL) emission, but also acts as an alternative reaction channel for static electron transfer (Hu et al, 2021;Shan et al, 2021;Tao et al, 2021). Considering the ubiquitous properties of structural water molecules (SWs) at heterogeneous interface and the universality of our PBIS model, we performed the XPS measurement of O 1S to test the presence of species of SWs for three typical metal NCs of Ag 0 Au@DT and Ag 0.5 Au@DT and Ag 4 Au@DT NCs (Figure 4B).…”

“…Obviously, the overlapping degree of two O atoms in the varied SWs, i.e., the stability of two type of SWs as emitters, determines the abnormal relation of long-wavelength emission with short-wavelength excitation (Figures 4A, 5) and their varied lifetimes of dual-emissions (Figure 1D), and this also answers the physical origins of two adsorption bands at 350 and 390 nm with corresponding excitation bands at 390 and 320 nm with π→π* transition characteristic due to the space interactions of p orbitals of two neighboring O atoms. The presence of SWs with the varied stability and multiple intermediate states at nanoscale interface probably answers the promoting role of alkali metal ion and hydroxyl group on the electro-catalytic reaction of water splitting (HER and OER), the selective reduction of CO 2 and α, β-unsaturated aldehydes, and the water-gas shift reaction (WGSR) by providing the alternative channels for concerted proton and electron transfer (Hu et al, 2021;Shan et al, 2021;Tao et al, 2021). In addition, due to the strong overlapping of p orbitals between two oxygen atoms in the SWs at confined nanoscale interface, the polarity of O-H bonds in individual water molecules is significantly decreased, even close to zero, which accounts for the anomalously low dielectric constant of water confined under extreme confinement (Fumagalli et al, 2018;Coudert, 2020;Coudert et al, 2021;Geim, 2021).…”

“…The discovery of these dynamic interface states also provides a completely new insight to understand the nature of heterogeneous catalysis and/or interface state (bonding), beyond the conventional metal-centered d band theory. (Hu et al, 2021;Shan et al, 2021;Tao et al, 2021;Medford et al, 2015;Liu et al, 2018) ]…”

“…Since the adsorption of SWs at the nanoscale interface is a ubiquitous phenomenon in nature, the concept of "SWs as emitters" could be used as a base model to elucidate the origin of PL of other low-dimensioned quantum dots, such as carbon, semiconductor, and perovskites type materials. In addition, the concept of "surface electronic states" formed by space overlapping of p orbitals of O atoms in SWS could act as an alternative channel for concerted electron and proton transfer, which provide new insights for an indepth understanding of heterogeneous catalysis and/or the nature of interface states (or interfacial bonding) (Hu et al, 2020;Hu et al, 2021;Shan et al, 2021;Tao et al, 2021).…”

Activation of H2O tailored by interfacial electronic states at nanoscale interface for enhanced electrocatalytic hydrogen evolution

“…This new formed surface transient state could be acted as an alternative channel for concerted electron and proton transfer at nanoscale interface. In fact, using our newly developed PBIS model, we have successfully explained the catalytic conversion mechanism of selective hydrogenation of organic compounds containing unsaturated functional groups such as nitro and carbonyl groups involving multiple electronproton transfer at the molecular level [47][48][49] . Since the electron and proton transfer process of traditional metal nanocatalysts for selective reduction of organic compounds containing nitro-groups is very similar to that of HER of electrocatalyst of metal nanoparticles, the working mechanism of micro-kinetics of both reactions should follow the same working mechanism.…”