Tuning aldol condensation product selectivity by controlling diffusion and reaction rates in zeolites

•Titration/modeling method for quantification of mass-transfer limitations in zeolites.•Non-linear variation of rate Vs titrated sites reveals mass-transport limitations.•Thiele modulus analysis reveals differences in MTL between ZSM-5 and Y zeolites.•Higher diffusional barriers for CPO than ACE are reflected in cross-condensation selectivity.•Site density manipulation allows tuning selectivity for self- and cross-condensation.