Tuning the Aggregates of Thiophene-based Trimers by Methyl Side-chain Engineering for Photocatalytic Hydrogen Evolution.

Organic π-conjugated semiconductors (OCSs) have recently emerged as a promising alternative to traditional inorganic materials for photocatalysis. However, the aggregation of OCSs in photocatalytic aqueous solution caused by self-assembly, which closely relates to the photocatalytic activity, has not yet been studied. Here, the relationship between the aggregation of 4,7-Bis(thiophen-2-yl) benzothiadiazole (TBT) and the photocatalytic activity was systematically investigated by introducing and varying the position of methyl side chains on the two peripheral thiophene units. Experimental and theoretical results indicated that the introduction of -CH3 group at the 3-position of TBT resulted in the smallest size and best crystallinity of aggregates compared to that of TBT, 4- and 5-positions. As a result, TBT-3 exhibited an excellent photocatalytic activity towards H2 evolution, ascribed to the shorten charge carrier transport distance and solid long-range order. These results suggest the important role of aggregation behavior of OCSs for efficient photocatalysis.

Grafting nanometer metal/oxide interface towards enhanced low-temperature acetylene semi-hydrogenation.

Metal/oxide interface is of fundamental significance to heterogeneous catalysis because the seemingly "inert" oxide support can modulate the morphology, atomic and electronic structures of the metal catalyst through the interface. The interfacial effects are well studied over a bulk oxide support but remain elusive for nanometer-sized systems like clusters, arising from the challenges associated with chemical synthesis and structural elucidation of such hybrid clusters. We hereby demonstrate the essential catalytic roles of a nanometer metal/oxide interface constructed by a hybrid Pd/Bi2O3 cluster ensemble, which is fabricated by a facile stepwise photochemical method. The Pd/Bi2O3 cluster, of which the hybrid structure is elucidated by combined electron microscopy and microanalysis, features a small Pd-Pd coordination number and more importantly a Pd-Bi spatial correlation ascribed to the heterografting between Pd and Bi terminated Bi2O3 clusters. The intra-cluster electron transfer towards Pd across the as-formed nanometer metal/oxide interface significantly weakens the ethylene adsorption without compromising the hydrogen activation. As a result, a 91% selectivity of ethylene and 90% conversion of acetylene can be achieved in a front-end hydrogenation process with a temperature as low as 44 °C.

Addressing the uncertainty of DFT-determined hydrogenation mechanisms over coinage metal surfaces.

Density functional theory (DFT) has been considered as a powerful tool for the identification of reaction mechanisms. However, it is still unclear whether the error of DFT calculations would lead to mis-identification of mechanisms. Here, taking the hydrogenation of acetylene and 1,3-butadiene as model reactions and employing a well-trained Bayesian error estimation functional with van der Waals correlation (BEEF-vdW), we try to estimate the error of DFT calculation results statistically, and therefore predict the reliability of the hydrogenation mechanisms identified. With an ensemble of 2000 functionals obtained around the BEEF-vdW functional as well as a descriptor developed to represent the possibility of different mechanisms, we found that the non-Horiuti-Polanyi mechanism is preferred on Ag(211) and Au(211), while the Horiuti-Polanyi mechanism is dominant on Cu(211). We further discovered that the descriptor is linearly correlated with the adsorption energies of reaction intermediates during acetylene and butadiene hydrogenation, and the hydrogenation of strongly adsorbed species are more likely to follow the Horiuti-Polanyi mechanism. We found the probability of following the non-HP mechanism obeys the order Cu(211) < Au(211) < Ag(211). Our work gives a more comprehensive explanation for the mechanisms of coinage metal catalyzed hydrogenation reactions, and also provides more theoretical insights into the development of new high-performance catalysts for selective hydrogenation reactions.

Correction: Fast prediction of oxygen reduction reaction activity on carbon nanotubes with a localized geometric descriptor.

Correction for 'Fast prediction of oxygen reduction reaction activity on carbon nanotubes with a localized geometric descriptor' by Kunran Yang et al., Phys. Chem. Chem. Phys., 2020, 22, 890-895, DOI: 10.1039/C9CP04885E.

Fast prediction of oxygen reduction reaction activity on carbon nanotubes with a localized geometric descriptor.

The oxygen reduction reaction (ORR) is a process of primary importance in fuel cell technology. The efficiency of carbon-based materials in this field has been already confirmed by many experimental studies, especially when doped with nitrogen or boron. In this work, we propose a localized geometric descriptor, based on the pyramidalization angle to report ORR activity on carbon nanotubes (CNTs). Our descriptor reflects the local curvature of the surface and the torsion of the π orbital system. We showed that the surface reactivity is directly related to the pyramidalization angle at the active sites. Nitrogen and boron doping makes it possible to reach a low overpotential for weakly curved surfaces, whereas for undoped surfaces the ideal ORR activity is only reached for highly curved CNTs. Consequently, the optimal size of the nanotube is determined by the doping type. Hence, we demonstrated a high statistical quality correlation between the adsorption energies of surface species and the pyramidalization angle at the active site. Our descriptor enables ready identification of the optimal diameter and the best doping type for the CNT surfaces, which is not possible with usual descriptors such as OH species adsorption. As a result, ORR geometric descriptors are very promising since their performance is comparable to that of electronic descriptors. In addition, they are less time-demanding in computation, and they are less sensitive to the accuracy of the calculation method.

Surface restructuring of Cu-based single-atom alloy catalysts under reaction conditions: the essential role of adsorbates.

The stabilities and catalytic performances of single-atom alloy (SAA) structures under the reaction conditions of acetylene hydrogenation are thoroughly examined utilizing density functional theory (DFT) calculations. Four Cu-based alloys with stable SAA structures reported before, namely PdCu, PtCu, RhCu and NiCu alloys, are investigated here. We find that the SAA structures of PdCu and PtCu are stable during the reaction, whilst the RhCu-SAA and NiCu-SAA structures are thermodynamically unstable upon acetylene adsorption and surface restructuring through the aggregation of the Rh and Ni atoms on the surfaces may also happen. It is also found that all the investigated structures of RhCu and NiCu alloys may give rise to the further hydrogenation of ethylene. However, desorption of ethylene is favored over the PdCu-SAA and PtCu-SAA surfaces, indicating that acetylene could be selectively hydrogenated to ethylene over these two surfaces, which is consistent with the experimental observations reported in the literature. Our work provides new understandings regarding SAA surface structures under reaction conditions and their catalytic reaction performances upon aggregation of the doped metal atoms.

Soluble organic nanotubes for catalytic systems.

In this paper, we report a novel method for constructing a soluble organic nanotube supported catalyst system based on single-molecule templating of core­shell bottlebrush copolymers. Various organic or metal catalysts, such as sodium prop-2-yne-1-sulfonate (SPS), 1-(2-(prop-2-yn-1-yloxy)ethyl)-1H-imidazole (PEI) and Pd(OAc)2 were anchored onto the tube walls to functionalize the organic nanotubes via copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction. Depending on the 'confined effect' and the accessible cavity microenvironments of tubular structures, the organic nanotube catalysts showed high catalytic efficiency and site-isolation features. We believe that the soluble organic nanotubes will be very useful for the development of high performance catalyst systems due to their high stability of support, facile functionalization and attractive textural properties.