Lee Hsun Lecture Series
Topic: Carbon materials as metal-free catalysts
Speaker: Prof. José L. Figueiredo
Laboratory of Catalysis and Materials - Associate Laboratory LSRE-LCM,
Faculty of Engineering, University of Porto, Portugal
Time: 10:00-12:00, (Mon.) Dec. 1, 2014
Venue: Room 403, Shi Changxu Building, IMR CAS
Welcome to attend!
The surface chemical properties of carbon materials are of paramount importance for their applications, particularly in catalysis. The structure of most carbons used in catalysis is graphenic, the unsaturated carbon atoms at the edges of the graphene layers and at basal plane defects being able to react with different compounds to form various types of surface functional groups. Such groups can play the role of active sites for catalysis, but they may also act as promoters or inhibitors, enhancing or diminishing the activity of the carbon catalyst, respectively. Indeed, carbon materials can be used as metal-free catalysts in acid-base or in redox processes. There is currently a considerable research activity on this topic, driven by the need to replace expensive metals and hazardous materials which are traditionally used in catalysis [1-3].
The nature and concentration of functional groups on the carbon surface can be modified by chemical and thermal treatments, or during the synthesis steps. Oxygenated groups can be introduced by treatment with oxidizing agents, either in the liquid phase or in the gas phase. Carbons with nitrogen functionalities can be obtained by carbonization of nitrogen-containing precursors or by post-treatments, while functionalization with sulfonic acid groups is usually achieved by treatment of the carbon material with sulphuric acid. Controlled thermal treatments can then be used for tuning the surface chemistry of the carbon materials by selectively removing undesired groups, or to prepare samples with different amounts of the desired groups. The advantage of this procedure is that the textural properties are not changed significantly, so that a set of carbon materials can be obtained with the same textural properties and different surface chemistries. X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD) are the most suitable methods for quantitative analysis of the surface groups [1,4].
Relevant examples of catalysis with carbon materials will be reviewed, focusing on the research done in the author’s group and emphasizing the role of the surface chemistry. Correlations of catalytic activity were established in a few cases, the corresponding turnover frequencies (TOF) allowing to benchmark the novel metal-free catalysts with those currently in use.
1) Serp P, Figueiredo JL (editors). Carbon Materials for Catalysis. John Wiley, Hoboken, NJ, 2009.
2) Figueiredo JL, Pereira MFR, Catal. Today, 2010; 150: 2-7.
3) Figueiredo JL, J. Mater. Chem. A, 2013; 1: 9351-9364.
4) Figueiredo JL, Pereira MFR, Freitas MMA, Órfão JJM, Carbon, 1999; 37: 1379-1389.