Descriptors for High-Performance Nitrogen-Doped Carbon Catalysts in Acetylene Hydrochlorination

Abstract

Nitrogen-doped carbons are promising materials for a broad range of applications. However, their rational design is greatly hampered by the lack of efficient methods to control the nitrogen speciation, which not only causes controversy about the roles of specific nitrogen functionalities, but also hinders investigations into other physicochemical characteristics of these materials. We herein present a cutting-edge strategy that allows a systematic tuning of the electrical conductivity of polyaniline-derived N-doped carbons at a defined nitrogen speciation and content, and similar porous properties. By applying these model systems in acetylene hydrochlorination, a major industrial technology for the production of polyvinylchloride, we provide insights into the active sites and the reaction mechanism and disclose two key catalytic descriptors for N-doped carbons in this reaction: (i) a high content of pyrrolic-N functionalities, promoting the adsorption of the reactants, and (ii) good electrical conductivity, likely influencing the surface diffusion of adsorbed species. The adverse correlation of the two descriptors to calcination temperature causes a trade-off that determines the catalytic activity. This understanding enabled the design of the first N-doped carbon catalyst that rivals the unprecedented activity of benchmark gold-based systems in acetylene hydro-chlorination.

The Multifaceted Reactivity of Single‐Atom Heterogeneous Catalysts

“…Forpractical application, SAAs are also supported and may thus present different inequivalent atoms depending on both the relative metal concentration and the size and morphology of the NPs. [41] There is some indication that metals can become encapsulated in the bulk of carbon-based supports,w hich may also lead to reduced specific activity. In carbon-based hosts and related materials the most favorable coordination sites are usually heteroatoms (N,O , S, or P).…”

Nitrogen‐Doped Carbons with Hierarchical Porosity via Chemical Blowing Towards Long‐Lived Metal‐Free Catalysts for Acetylene Hydrochlorination

“…Still, carbon materials, including defect‐rich carbons, graphitic carbon nitride, and heteroatom‐doped carbons ( i. e ., N, P, B, S) are highly desirable alternatives, owing to their significant environmental and cost advantages compared to metal‐based catalysts . In particular, nitrogen‐doped carbons (NCs), derived via carbonization of C/N‐precursors ( i. e ., polyaniline, polydopamine, ZIF‐8), stand out as the most promising candidates, rivaling the initial activity of their metal‐based analogues at elevated reaction temperatures . Despite these encouraging results, the applicability of NCs is hindered by their insufficient durability under relevant process conditions ( T =403‐453 K, P =1.5 bar, HCl : C 2 H 2 =1.1 : 1) .…”

“…Despite these encouraging results, the applicability of NCs is hindered by their insufficient durability under relevant process conditions ( T =403‐453 K, P =1.5 bar, HCl : C 2 H 2 =1.1 : 1) . In particular, pore blockage through the formation of carbonaceous residues has been identified as the major reason for catalyst deactivation . A possible strategy to mitigate the impact of coke species is to enhance the micropore volume and introduce auxiliary pores to improve the accessibility of the active sites within the micropores and facilitate the molecular diffusion of reactants, intermediates, and products.…”

“…Consequently, the hampered desorption of VCM might account for the comparably lower activity of NC‐III. As expected, NC‐I rapidly deactivates with time‐on‐stream ( tos , linearized deactivation constant k D =20 h −1 , derived via linear regression of the initial 5 h tos ), at a rate slightly higher compared to benchmark polyaniline‐derived N‐doped carbon (NC, k D =14 h −1 , Figure S9) . Remarkably, the stability of NC‐II and NC‐III is ca .…”

Three‐Dimensional Interconnected Porous Nitrogen‐Doped Carbon Hybrid Foam for Notably Promoted Direct Dehydrogenation of Ethylbenzene to Styrene

“…[33][34][35][36][37][38] Styrene, an important chemical monomer for the synthesis of polymers like polystyrene, is primarily produced from direct dehydrogenation of ethylbenzene over commercial potassium-promoted iron oxide at the present. [43][44][45] In consideration of aforementioned advantages and good regenerability, environmentally friendly character, carbon materials have shown enormous potential to alternate conventional catalysts in the requirements of green chemistry, [14,[46][47][48] and have experienced an unprecedented development for novel material design and industrial application. Although high styrene selectivity and yield are achieved, massive energy and water consumption are still harmful to the environment, thus a clean and economic ethylbenzene dehydrogenation process and efficient catalyst are of great demand for the production of styrene.…”