Can Temperature-Programmed Techniques Provide the Gold Standard for Carbon Surface Characterization?

Abstract

Due to their chemical and thermal stability, electrical conductivity, and high specific surface areas, nanocarbons and porous carbon materials have found use in numerous key applications within the current transition of energy and raw-material sources. Since all these applications rely on multiphase interactions between the carbon surface and surrounding solid, liquid, or gaseous phases, carbon surface chemistry is elevated to a critical factor of influence. However, the characterization of carbon surface chemistry is notoriously complex, involving carbon defect sites and chemically similar heteroatom species in a wide range of different binding states and chemical environments. Due to this high degree of complexity, a comprehensive characterization of carbon surface species and reactivity is a major challenge for which there is no analytical “silver bullet” but is fundamental to the rational development of advanced functional carbon materials. In this context we would like to highlight the potential of temperature-programmed techniques (TPX) for carbon surface analytics, which benefit from widely available, easy-to-handle equipment and offer information on the identity, quantity, and reactivity of surface species. Hence, this article reviews the state of the art concerning temperature-programmed techniques for carbon surface characterization, focusing not only on the qualitative and quantitative analysis of carbon surface species but also on the unique ability of temperature-programmed methods to assess carbon surface reactivity. In this context, progress made so far in temperature-programmed desorption, temperature-programmed reduction, and temperature-programmed surface reactions is discussed, highlighting pitfalls and gaps in knowledge. Based on this foundation, strategies for the further development of temperature-programmed methods for carbon surface analysis are proposed, aiming to establish TPX as the future gold-standard in carbon surface characterization.

Quantifying Carbon Active Sites Chemisorbing Hydrogen on Oxygen Containing Activated Carbons during Heat Treatment in Hydrogen Atmosphere

“…In this study, the fate of OFGs desorbed as CO gas during heat treatment in a hydrogen atmosphere was identified by a combination of TPD and TPR techniques, which are still in their infancy. 59 After quantifying the chemisorbed H 2 on the carbons and correlating the abovementioned results, the specific conditions for the generation of carbon active sites chemisorbing hydrogen were quantitatively evaluated.…”

“…Owing to the difficulties in the precise analysis of evolved gases such as CO, CO 2 , H 2 , CH 4 , and H 2 O, and the complexity of the secondary reactions during temperature-programmed desorption (TPD) and/or Temperature-programmed reaction (TPR), the behavior of the H 2 reaction with carbons containing different type/number of OFGs , and particularly the nature of the generated carbon active sites is not yet clear. In this study, the fate of OFGs desorbed as CO gas during heat treatment in a hydrogen atmosphere was identified by a combination of TPD and TPR techniques, which are still in their infancy . After quantifying the chemisorbed H 2 on the carbons and correlating the above-mentioned results, the specific conditions for the generation of carbon active sites chemisorbing hydrogen were quantitatively evaluated.…”

Aqueous Phase Reforming over Platinum Catalysts on Doped Carbon Supports: Exploring Platinum–Heteroatom Interactions

“…The heat treatment of the CNF-ox allowed the formation of defects on the surface by decomposition of oxygen containing groups to CO and CO 2 at 700 °C, resulting in a higher-surface area . Similarly, during S doping, a comparatively high carbon gasification rate may lead to an increase in the surface area . The textural changes of N-CNF, B-CNF, and P-CNF can be referred to a decrease in the total pore volume, as shown by lower N 2 uptake in the adsorption isotherms (Figure S5).…”

Interface Engineering for High-Performance Thermoelectric Carbon Nanotube Films

“…Typically, a CO 2 peak results from carboxylic acid at below 600 °C, or lactones at above 600 °C; phenols, ethers, and carbonyls (and quinones) originate a CO peak; carboxylic anhydrides originate both a CO and a CO 2 peak; a NH 3 peak results from amino groups or amide. 44 Obviously, carboxylic groups in CNT-COOH first decomposed at around 380 and 550 °C, by releasing CO 2 . In contrast, the decomposition of lactone, carbonyl, and phenol groups occurred at higher temperatures.…”

“…The literature provides a specific temperature range for the functional groups on nanocarbon materials. Typically, a CO 2 peak results from carboxylic acid at below 600 °C, or lactones at above 600 °C; phenols, ethers, and carbonyls (and quinones) originate a CO peak; carboxylic anhydrides originate both a CO and a CO 2 peak; a NH 3 peak results from amino groups or amide . Obviously, carboxylic groups in CNT-COOH first decomposed at around 380 and 550 °C, by releasing CO 2 .…”