n-Dodecane steam reforming over Ni catalysts supported on ZrO₂–KNbO₃

Coke-resistant Ni catalyst supports are evaluated for steam reforming (SR) n-dodecane, the alkane used as a surrogate for diesel fuel in this study. Reactions are conducted at 800 °C for 5 h, with a molar steam-to-carbon ratio of 3.0 and a gas hourly space velocity of 20000 h⁻¹. Thermally stable, coke-resistant supports loaded with 15 wt% Ni are prepared using the following potassium oxides: K₂Ti₂O₅ (KTI), K₄Zr₅O₁₂ (KZR), KNbO₃ (KNB), KTaO₃ (KTA), and K₂WO₄ (KW). Ni/KZR and Ni/KW show the best catalytic performance in the SR reaction due to their moderate-to-strong acidities and lack of porosity, which are necessary features for hydrocarbon cracking. Unfortunately, these catalysts are poorly stable under the defined operating conditions. KNB is the most suitable support due to its excellent thermal stability and coke-resistance; however, it lacks acidity. The acidity of KNB is enhanced by impregnation with ZrO₂, which transforms it into an acidic oxide (ZR-KNB). ZR-KNB features high thermal stability and high coke-resistance during the SR of n-dodecane under the applied test conditions. The Ni/ZR-KNB catalyst delivers excellent SR performance with respect to both n-dodecane conversion and hydrogen selectivity.