Gioria Esteban, Ocampo-Restrepo Vivianne K, Bjørnlund Anton Simon, Pedersen Verdande Kim, Helveg Stig, Chorkendorff Ib, Damsgaard Christian Danvad
Department of Physics, Technical University of Denmark, Lyngby, 2800 Kgs, Denmark.
Center for Visualizing Catalytic Processes (VISION), Department of Physics, Technical University of Denmark, Lyngby, 2800 Kgs, Denmark.
Small. 2025 Aug;21(31):e2500994. doi: 10.1002/smll.202500994. Epub 2025 Jun 4.
The emerging trends in carbon nanotube applications make them exceptional functional materials of highly added value. Thermocatalytic CH decomposition is an effective pathway toward their production, forming H as the only byproduct. However, catalyst deactivation due to sintering and blockage of the active sites, together with their detachment from the support remains a challenge. In this work, nickel phyllosilicate is employed as a catalyst precursor for the formation of active and stable metal sites. Surprisingly, the particles remain attached to the support, switching from the typical tip-growth reported for state-of-the-art catalysts to a base growth mechanism. The nickel nanoparticles remain stable against sintering even under harsh conditions up to 750 °C. A combination of DFT calculations, in situ TEM, and in situ XRD studies reveals that the reduction of Ni─O bonds, particularly those involving silicon-bonded oxygen (Si─O─Ni; apical oxygen), requires high temperatures. Post-activation, the small, dispersed nickel nanoparticles catalyze CH decomposition into carbon nanotubes and H. Unlike prior reports, in situ XRD confirms no nickel carbide formation in the bulk. Additionally, in contrast to any known nickel-based catalyst, it is demonstrated that particles below 10 nm can effectively activate CH cracking, avoid encapsulation, and enable the base-growth of micrometer-long, narrow carbon nanotubes.
碳纳米管应用中的新兴趋势使其成为具有高附加值的特殊功能材料。热催化CH分解是其生产的有效途径，仅形成H作为副产物。然而，由于烧结和活性位点堵塞导致的催化剂失活，以及它们与载体的分离仍然是一个挑战。在这项工作中，镍层状硅酸盐被用作形成活性和稳定金属位点的催化剂前体。令人惊讶的是，颗粒仍附着在载体上，从最先进催化剂报道的典型尖端生长转变为基部生长机制。即使在高达750°C的苛刻条件下，镍纳米颗粒也能保持稳定不烧结。密度泛函理论计算、原位透射电子显微镜和原位X射线衍射研究的结合表明，Ni─O键的还原，特别是那些涉及硅键合氧（Si─O─Ni；顶端氧）的键，需要高温。活化后，小的、分散的镍纳米颗粒催化CH分解为碳纳米管和H。与先前的报道不同，原位X射线衍射证实本体中没有碳化镍形成。此外，与任何已知的镍基催化剂相比，已证明尺寸小于10 nm的颗粒可以有效激活CH裂解，避免包封，并实现微米长、窄碳纳米管的基部生长。
