SiO2 core supports are prepared via the Stöber method with various synthesizing solvents. Then, a Ni shell is deposited on SiO2 by a deposition–precipitation method. The results illustrate that using isopropanol as the solvent governs the catalyst particle size with a superior dispersion and a high catalytic activity. Thus, the calcination atmosphere of the catalyst directly affects both the chemical state and the catalytic performance of the active sites. The Ni@SiO2‐I‐air (isopropanol) catalyst calcined by air with more Ni2+ facilitates the highest H2 production of 142.2 mmol g−1 h−1 but provides a carbon nanotube (CNT) yield of only 7.6%. Most importantly, the Ni@SiO2‐I‐H2 catalyst calcined by ambient H2 is prone to form Ni0 species, thus providing the best crystalline conversion and metal–support interaction, which benefits the production of CNTs to a maximum yield of 19.8% with a H2 production of 122.8 mmol g−1 h−1.