An overview on the carbon deposited during dry reforming of methane (DRM): Its formation, deposition, identification, and quantification

• Characteristics of graphitic, amorphous, and filamentous carbon were revealed. • Operational and catalytic effects on carbon formation and deposition were unveiled. • Techniques to identify and quantify deposited carbon were reviewed. Carbon deposition in dry reforming of methane (DRM) is associated with two side reactions: CH 4 decomposition and Boudouard reaction. Effective management of DRM technology necessitates a thorough comprehension of associated side reactions. In view of this, the current review systematically provides insights into carbon in DRM, with its formation, deposition, identification, qualitative and quantitative determinations highlighted herein. Under most occasions, the carbon formed and deposited can be broadly categorized into graphitic, amorphous and filamentous forms, each with varied resilience under regenerative conditions. Therefore, correctly identifying the genre of deposited carbon serves the first vital step to effective carbon gasification and formulating appropriate catalytic regeneration strategies. While presenting the main characteristic of each carbon species, the reliance of their formation kinetics on different factors, namely temperature, pressure, inlet feed (reactants composition and CH 4 -to-CO 2 ratio), catalyst genre, etc., were highlighted in this review too. In brief, elevated temperatures and pressures, catalyst formulation and CH 4 /CO 2 ratio impact graphitic build-up, decarbonization, and carbon reactivity, crystallinity, and quantity. Meanwhile, characterization techniques that provide valuable insights into the deposited carbon species were identified too, with emphasis placed on those unveiling crystallinity, morphological, structural, thermal stability, reactivity and quantity of deposited carbon. Understanding the features of deposited carbon is crucial, particularly for DRM reaction that suffers severely from this hindrance. Despite advances in understanding carbon species in DRM, strategies to control carbon species formation mechanisms towards reactive carbon formation remain underdeveloped, emphasizing the need for continued research by experienced and new researchers in the DRM community.