K k, r R = rate of reaction S T = temperature X = dimensionless pellet radius Y = dimensionless temperature = activity distribution function defined by Eq. 2 = effective thermal conductivity of catalyst pellet = radius of catalyst pellet = selectivity towards the desired reaction Greek Letters a P Y AH 1 (T = parameter defining activity profile according to Eq. 2 = heat of reaction parameter defined by Eq. 14 = dimensionless activation energy = standard enthalpy change of reaction = effectiveness factor = starvation parameter defined by Eq. 10 = modified Thiele modulus defined by Eq. 8 = dimensionless surface rate constant defined by Eq. 7 Subscripts 1,2 S = designates surface conditions = designate desired and undesired reactions