Letter pubs.acs.org/acscatalysis
Carbon Dioxide Hydrogenation over a Metal-Free Carbon-Based Catalyst Jingjie Wu,†,∇ Cun Wen,‡,∇ Xiaolong Zou,§ Juan Jimenez,‡ Jing Sun,∥ Yujian Xia,⊥ Marco-Tulio Fonseca Rodrigues,† Soumya Vinod,† Jun Zhong,⊥ Nitin Chopra,# Ihab N. Odeh,# Guqiao Ding,∥ Jochen Lauterbach,*,‡ and Pulickel M. Ajayan*,† †
Department of Materials Science and NanoEngineering, Rice University, Houston, Texas 77005, United States Department of Chemical Engineering, University of South Carolina, Columbia, South Carolina 29201, United States § Tsinghua-Berkeley Shenzhen Institute, Tsinghua University, Shenzhen, Guangdong 518055, China ∥ State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050, China ⊥ Institute of Functional Nano and Soft Materials Laboratory (FUNSOM), Soochow University, Suzhou 215123, China # Saudi Basic Industries Corporation (SABIC), Sugar Land, Texas 77478, United States ‡
S Supporting Information *
ABSTRACT: The hydrogenation of CO2 into useful chemicals provides an industrial-scale pathway for CO2 recycling. The lack of effective thermochemical catalysts currently precludes this process, since it is challenging to identify structures that can simultaneously exhibit high activity and selectivity for this reaction. Here, we report, for the first time, the use of nitrogendoped graphene quantum dots (NGQDs) as metal-free catalysts for CO2 hydrogenation. The nitrogen dopants, located at the edge sites, play a key role in inducing thermocatalytic activity in carbon nanostructures. Furthermore, the thermocatalytic activity and selectivity of NGQDs are governed by the doped N configurations and their corresponding defect density. The increase of pydinic N concentration at the edge site of NGQDs leads to lower initial reaction temperature for CO2 reduction and also higher CO2 conversion and selectivity toward CH4 over CO. KEYWORDS: CO2 hydrogenation, graphene quantum dots, N doping, methane
■
chemicals.10−12 The main products obtained after this reduction process are carbon monoxide (CO), methanol (CH3OH), and methane (CH4), in proportions that are highly dependent on the choice of catalysts.13 The direct transformation of CO2 into CH3OH is the ideal pathway, but is very limited by the lack of efficient catalysts. Although the Cu/ZnO/ Al2O3 catalyst shows promising selectivity and space-time yield for CH3OH production, the process requires a pressure of 36 MPa, which is likely too high for commercial operation.14 An alternative approach is the production of CO via the reverse water−gas shift (RWGS) reaction. CO produced via this pathway could subsequently be used as feedstock for the Fischer−Tropsch synthesis of fuels. Many metal catalysts, such as Co, Pd, and Rh, and carbide (Mo2C) exhibit satisfactory selectivity (70%−90%) toward CO formation in the RWGS reaction, but they suffer from low CO2 conversion (
