The greenhouse effect and global warming are serious problems because the increasing global demand for fossil fuels has led to a rapid rise in greenhouse gas exhaust emissions in the atmosphere and disruptive changes in climate. As a major contributor, CO₂ has attracted much attention from scientists, who have attempted to convert it into useful products by electrochemical or photoelectrochemical reduction methods. Facile design of efficient but inexpensive and abundant catalysts to convert CO₂ into fuels or valuable chemical products is essential for materials chemistry and catalysis in addressing global climate change as well as the energy crisis. Herein, we show that two-dimensional fewlayer graphitic carbon nitride (g-C₃N₄) can function as an efficient metal-free electrocatalyst for selective reduction of CO₂ to CO at low overpotentials with a high Faradaic efficiency of ~ 80%. The polarized surface of ultrathin g-C₃N₄ layers (thickness: ~ 1 nm), with a more reductive conduction band, yields excellent electrochemical activity for CO₂ reduction.

In this work, we described a proof-of-concept method to promote the activity and selectivity of Pd nanoparticles for heterogeneous catalysis (exemplified by C–C coupling reactions) by using acid sites within a zeolite framework. The Pd nanoparticles were encapsulated inside the crystalline walls of mesoporous H-ZSM-5 leading to hybrid samples (denoted as Pd@mZ-x-H) with controlled number of acid sites. A linear relationship between the number of acid sites of the zeolite nanocrystals and the catalytic activities of the Pd nanoparticles in organic reactions was established. Moreover, the shape-dependent selectivity of Pd@mZ-x-H was not sacrificed when the final activity was enhanced.

A facile method was developed to fabricate nitrogen-doped graphene microtubes (N-GMT) with ultra-thin walls of 1–4 nm and large inner voids of 1–2 μm. The successful introduction of nitrogen dopants afforded N-GMT more active sites for significantly enhanced hydrogen evolution reaction (HER) activity, achieving a current density of 10 mA·cm^–2 at overpotentials of 0.464 and 0.426 V vs. RHE in 0.1 and 6 M KOH solution, respectively. This HER performance surpassed that of the best metal-free catalyst reported in basic solution, further illustrating the great potential of N-GMT as an efficient HER catalyst for real applications in water splitting and chlor-alkali processes.