Junrui Li

Pd Nanoparticles Coupled to WO2.72 Nanorods for Enhanced Electrochemical Oxidation of Formic Acid

We synthesize a new type of hybrid Pd/WO2.72 structure with 5 nm Pd nanoparticles (NPs) anchored on 50 × 5 nm WO2.72 nanorods. The strong Pd/WO2.72 coupling results in the lattice expansion of Pd from 0.23 to 0.27 nm and the decrease of Pd surface electron density. As a result, the Pd/WO2.72 shows much enhanced catalysis toward electrochemical oxidation of formic acid in 0.1 M HClO4; it has a mass activity of ∼1600 mA/mgPd in a broad potential range of 0.4-0.85 V (vs RHE) and shows no obvious activity loss after a 12 h chronoamperometry test at 0.4 V. Our work demonstrates an important strategy to enhance Pd NP catalyst efficiency for energy conversion reactions.

AgPd Nanoparticles Deposited on WO2.72 Nanorods as an Efficient Catalyst for One-Pot Conversion of Nitrophenol/Nitroacetophenone into Benzoxazole/Quinazoline

We report a seed-mediated growth of 2.3 nm AgPd nanoparticles (NPs) in the presence of 40 × 5 nm WO2.72 nanorods (NRs) for the synthesis of AgPd/WO2.72 composites. The strong interactions between AgPd NPs and WO2.72 NRs make the composites, especially the Ag48Pd52/WO2.72, catalytically active for dehydrogenation of formic acid (TOF = 1718 h-1 and Ea = 31 kJ/mol) and one-pot reactions of formic acid, 2-nitrophenol, and aldehydes into benzoxazoles in near quantitative yields under mild conditions. The catalysis can also be extended to the one-pot reactions of ammonium formate, 2-nitroacetophenone, and aldehyde for high yield syntheses of quinazolines. Our studies demonstrate a new catalyst design to achieve a green chemistry approach to one-pot reactions for the syntheses of benzoxazoles and quinazolines.

Stabilizing CuPd Nanoparticles via CuPd Coupling to WO2.72 Nanorods in Electrochemical Oxidation of Formic Acid

Stabilizing a 3d-transition metal component M from an MPd alloy structure in an acidic environment is key to the enhancement of MPd catalysis for various reactions. Here we demonstrate a strategy to stabilize Cu in 5 nm CuPd nanoparticles (NPs) by coupling the CuPd NPs with perovskite-type WO2.72 nanorods (NRs). The CuPd NPs are prepared by controlled diffusion of Cu into Pd NPs, and the coupled CuPd/WO2.72 are synthesized by growing WO2.72 NRs in the presence of CuPd NPs. The CuPd/WO2.72 can stabilize Cu in 0.1 M HClO4 solution and, as a result, they show Cu, Pd composition dependent activity for the electrochemical oxidation of formic acid in 0.1 M HClO4 + 0.1 M HCOOH. Among three different CuPd/WO2.72 studied, the Cu48Pd52/WO2.72 is the most efficient catalyst, with its mass activity reaching 2086 mA/mgPd in a broad potential range of 0.40 to 0.80 V (vs RHE) and staying at this value after the 12 h chronoamperometry test at 0.40 V. The synthesis can be extended to obtain other MPd/WO2.72 (M = Fe, Co, Ni), making it possible to study MPd-WO2.72 interactions and MPd stabilization on enhancing MPd catalysis for various chemical reactions.

Fe Stabilization by Intermetallic L10-FePt and Pt Catalysis Enhancement in L10-FePt/Pt Nanoparticles for Efficient Oxygen Reduction Reaction in Fuel Cells

We report in this article a detailed study on how to stabilize a first-row transition metal (M) in an intermetallic L10-MPt alloy nanoparticle (NP) structure and how to surround the L10-MPt with an atomic layer of Pt to enhance the electrocatalysis of Pt for oxygen reduction reaction (ORR) in fuel cell operation conditions. Using 8 nm FePt NPs as an example, we demonstrate that Fe can be stabilized more efficiently in a core/shell structured L10-FePt/Pt with a 5 Å Pt shell. The presence of Fe in the alloy core induces the desired compression of the thin Pt shell, especially the two atomic layers of Pt shell, further improving the ORR catalysis. This leads to much enhanced Pt catalysis for ORR in 0.1 M HClO4 solution (at both room temperature and 60 °C) and in the membrane electrode assembly (MEA) at 80 °C. The L10-FePt/Pt catalyst has a mass activity of 0.7 A/mgPt from the half-cell ORR test and shows no obvious mass activity loss after 30 000 potential cycles between 0.6 and 0.95 V at 80 °C in the MEA, meeting the DOE 2020 target (<40% loss in mass activity). We are extending the concept and preparing other L10-MPt/Pt NPs, such as L10-CoPt/Pt NPs, with reduced NP size as a highly efficient ORR catalyst for automotive fuel cell applications.

Maximizing the Catalytic Activity of Nanoparticles through Monolayer Assembly on Nitrogen-Doped Graphene

We report a facile method for assembly of a monolayer array of nitrogen-doped graphene (NG) and nanoparticles (NPs) and the subsequent transfer of two layers onto a solid substrate (S). Using 3 nm NiPd NPs as an example, we demonstrate that NiPd-NG-Si (Si=silicon wafer) can function as a catalyst and show maximum NiPd catalysis for the hydrolysis of ammonia borane (H3 NBH3 , AB) with a turnover frequency (TOF) of 4896.8 h-1 and an activation energy (Ea ) of 18.8 kJ mol-1 . The NiPd-NG-S catalyst is also highly active for catalyzing the transfer hydrogenation from AB to nitro compounds, leading to the green synthesis of quinazolines in water. Our assembly method can be extended to other graphene and NP catalyst materials, providing a new 2D NP catalyst platform for catalyzing multiple reactions in one pot with maximum efficiency.

Surface Pd-rich PdAg nanowires as highly efficient catalysts for dehydrogenation of formic acid and subsequent hydrogenation of adiponitrile

The demand for nylon-66 has sharply increased in industry because of its high mechanical strength, high rigidity, and excellent stability. The deep hydrogenation of adiponitrile (ADN) to 1,6-hexanediamine (HDA) is considered as a crucial step to produce nylon-66 in industry. Herein, we report a diffusion strategy to prepare surface Pd-rich PdAg nanowires (NWs) via a seed-mediated growth in polyol solution for efficient dehydrogenation catalysis of formic acid (FA) and subsequent hydrogenation of ADN by using FA as an in situ hydrogen source. The composition of surface Pd-rich PdAg NWs could be easily tuned by controlling the amounts of the precursors. And the surface Pd-rich Pd5Ag5 NWs exhibit the highest activity for dehydrogenation catalysis of FA with an initial TOF of 1600 h−1 and a highly efficient hydrogenation of ADN to HDA with 99% selectivity and 99% conversion at 50 °C. Their enhanced catalytic performance could be attributed to the Pd-rich surface of the NWs and more efficient electron transfer from Ag to Pd. This work demonstrates a new way to prepare surface Pd-rich Pd5Ag5 NWs for deeply hydrogenating ADN to HDA with FA as an in situ hydrogen source.