Catalytic Decomposition of Pyrolysis Fuel Oil over in Situ Carbon-Coated Ferrierite Zeolite for Selective Hydrogen Production

Catalytic decomposition of pyrolysis fuel oils (PFO) for selective production of hydrogen without any significant formation of greenhouse gas (CO₂ and CH₄) was investigated using ferrierite (FER) zeolites with different Si/Al molar ratios. The hydrogen production rate based on the feed moles of PFO was maximized on the FER having a Si/Al molar ratio of 10.4, and the hydrogen production rate on the FER zeolites was well correlated with their amounts of strong acid sites which easily form the active coke intermediates. In situ generated crystalline coke precursors on the acidic FER(10) surfaces having larger amounts of defect sites further played an important role as catalytic active sites for PFO decomposition and reforming reaction of CH₄ generated as a main byproduct. The crystalline phases of the encapsulated graphitic carbon layers formed on the outer surfaces of the FER zeolites were strongly affected by their original acidic strengths, which simultaneously altered a steady-state hydrogen production rate with different product distributions of liquid-phase polycyclic aromatic components. Less amounts of amorphous polyaromatic chemicals were formed on the most active FER(10) by easy decomposition reactions of the cracked intermediates from PFO. Although the initial activity of catalytic PFO decomposition was well correlated with the number of acidic sites of FER zeolites, the steady-state production rate of pure hydrogen was significantly affected by the newly formed surface coke properties on the carbon-encapsulated FER such as its crystallinity and number of defect sites. The FER(10) showed a higher catalytic activity for PFO decomposition due to its abundant strong acidic sites and newly formed active graphitic carbon layers for a further CH₄ reforming reaction.