We investigated the cracking of n-decane and 2-ethylphenol as co-substrate in a 90/10 wt.-% mixture over zeolites Y and beta. The use of these substrates aimed to better understand the occurring chemistry in applications such as Co-FCC. We employed a number of different zeolites Y with different amounts of active sites and pore volumes. Additionally, the pore system of zeolite beta was modified by basic leaching. The materials were characterized by N-2 physisorption, ICP-OES, XRD, Al-27, H-1, C-13 MAS NMR, NH3-TPD, IR and TGA. It was found that the activity of the catalysts depends on the number of Bronsted acid sites as determined by NMR spectroscopy. Also most important is the mesopore volume/mesopore surface which is beneficial for the diffusion towards the micropores, especially for zeolite Y that is able to deoxygenate phenols.