Isolation of Cu Atoms in Pd Lattice: Forming Highly Selective Sites for Photocatalytic Conversion of CO2 to CH4.

Photocatalytic conversion of CO2 to CH4, a carbon-neutral fuel, represents an appealing approach to remedy the current energy and environmental crisis; however, it suffers from the large production of CO and H2 by side reactions. The design of catalytic sites for CO2 adsorption and activation holds the key to address this grand challenge. In this Article, we develop highly selective sites for photocatalytic conversion of CO2 to CH4 by isolating Cu atoms in Pd lattice. According to our synchrotron-radiation characterizations and theoretical simulations, the isolation of Cu atoms in Pd lattice can play dual roles in the enhancement of CO2-to-CH4 conversion: (1) providing the paired Cu-Pd sites for the enhanced CO2 adsorption and the suppressed H2 evolution; and (2) elevating the d-band center of Cu sites for the improved CO2 activation. As a result, the Pd7Cu1-TiO2 photocatalyst achieves the high selectivity of 96% for CH4 production with a rate of 19.6 µmol gcat-1 h-1. This work provides fresh insights into the catalytic site design for selective photocatalytic CO2 conversion, and highlights the importance of catalyst lattice engineering at atomic precision to catalytic performance.

Assessing heavy-duty vehicles (HDVs) on-road NOx emission in China from on-board diagnostics (OBD) remote report data.

Mobile source emissions are some of the major causes of air pollution across the world and are associated with numerous adverse health impacts. China has implemented increasingly stringent emission standards over the past few decades, the most recent one being the sixth emission standard (China VI) first rolled out in 2019. The China VI standard places special emphasis on tightening limits for NOx emission and introduces remote monitoring of vehicles' On-board diagnostics (OBD) data to reduce emissions from diesel and gas-powered heavy-duty vehicles (HDV). This paper aims to establish a methodology to calculate HDV NOx emissions on an extended timescale, and under real-world operations. OBD data was collected and examined from 53 China VI diesel HDVs and 14 China V diesel HDVs, which found that the average NOx emission factors are 1.420 g/km and 3.894 g/km for the two samples respectively; this indicates that the implementation of China VI standard helps to significantly reduce NOx emission from HDVs. Combining the emission factors and calculated travel distances collected by OBD and vehicle sales data, the China VI emission standard is estimated to have resulted in 43,969 tons of NOx emission reduction by the end of 2020. With China announcing country-wide enforcement of the new standard in 2021, >1.7 million tons of NOx emission could be avoided by 2023 annually.

Structural Reconstruction of Cu2 O Superparticles toward Electrocatalytic CO2 Reduction with High C2+ Products Selectivity.

Structural reconstruction is a process commonly observed for Cu-based catalysts in electrochemical CO2 reduction. The Cu-based precatalysts with structural complexity often undergo sophisticated structural reconstruction processes, which may offer opportunities for enhancing the electrosynthesis of multicarbon products (C2+ products) but remain largely uncertain due to various new structural features possibly arising during the processes. In this work, the Cu2 O superparticles with an assembly structure are demonstrated to undergo complicated structure evolution under electrochemical reduction condition, enabling highly selective CO2 -to-C2+ products conversion in electrocatalysis. As revealed by electron microscopic characterization together with in situ X-ray absorption spectroscopy and Raman spectroscopy, the building blocks inside the superparticle fuse to generate numerous grain boundaries while those in the outer shell detach to form nanogap structures that can efficiently confine OH- to induce high local pH. Such a combination of unique structural features with local reaction environment offers two important factors for facilitating C-C coupling. Consequently, the Cu2 O superparticle-derived catalyst achieves high faradaic efficiencies of 53.2% for C2 H4 and 74.2% for C2+ products, surpassing the performance of geometrically simpler Cu2 O cube-derived catalyst and most reported Cu electrocatalysts under comparable conditions. This work provides insights for rationally designing highly selective CO2 reduction electrocatalysts by controlling structural reconstruction.

Direct Z-Scheme 0D/2D Heterojunction of CsPbBr3 Quantum Dots/Bi2WO6 Nanosheets for Efficient Photocatalytic CO2 Reduction.

Photocatalytic CO2 reduction is an appealing approach to convert solar energy into high value-added chemicals. All-inorganic CsPbBr3 quantum dots (QDs) have emerged as a promising photocatalyst for reducing CO2. However, pristine CsPbBr3 has a low catalytic performance, mainly due to severe charge recombination. Herein, a 0D/2D heterojunction of CsPbBr3 QDs/Bi2WO6 nanosheet (CPB/BWO) photocatalysts is fabricated for photocatalytic CO2 reduction. The CPB/BWO photocatalyst achieves excellent photocatalytic performance: the total yield of CH4/CO is 503 µmol g-1, nearly 9.5 times higher than the pristine CsPbBr3. The CPB/BWO heterojunction also exhibits much-improved stability during photocatalytic reactions. On the basis of various characterization techniques, our investigations verified a direct Z-scheme charge migration mechanism between CsPbBr3 QDs and Bi2WO6 nanosheets. The improved photocatalytic performance is originated from the high spatial separation of photoexcited charge carriers in CPB/BWO, which can also preserve strong individual redox abilities of two components. This work reports an efficient direct Z-scheme heterojunction photocatalytic system based on metal halide perovskites. The novel strategy we proposed may bring up new opportunities for the development of metal halide perovskite photocatalysts with greatly enhanced activities.