This paper presents a predictive control design for diesel vehicle platoons, such as medium- and heavy-duty truck platoons, to achieve lower NOx emissions. By incorporating vehicle longitudinal dynamics control and powertrain estimation with aftertreatment system control, an enhanced emission performance can be attained for the entire platoon considering different operating conditions for individual vehicles. The proposed method utilizes exhaust gas predictive information within a preview horizon to generate optimal control actions such that the tradeoff between NOx reduction efficiency and NH3 slip in the aftertreatment systems can be well-managed. Performance improvement is demonstrated through simulation studies based on an experimental validated powertrain and aftertreatment system model.