NOVELTY - Exhaust after-treatment system comprises greater than or equal to 2 branches (111, 114) configured to receive separate portions of the exhaust; a nitrogen oxides adsorber-catalyst within at least one branch; a trailing conduit (112) configured to receive the exhaust from the branches; and an ammonia-selective catalytic reduction (SCR) catalyst within the trailing conduit.    USE - The exhaust after-treatment system is used for a power generation system useful for vehicle. It is used for treating engine exhaust (all claimed).    ADVANTAGE - The configuration provides a continuous (or near continuous) presence of oxygen within the trailing exhaust conduit, which improves the efficiency of the ammonia-SCR catalyst, and can simplify the operation of the clean-up oxidation catalyst. It has an improved reliability and provides reduction in peak flow rates that occur during regeneration so that catalyst requirement is reduced. It provides vehicles that meet strict emission control regulations.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for:    (1) power generation system (100) comprising an engine operable to produce an exhaust, and the exhaust after-treatment system (102) configured to treat the exhaust;    (2) vehicle comprising the power generation system;    (3) method of treating engine exhaust comprising channeling the exhaust through a leading exhaust conduit, splitting the exhaust from the leading exhaust conduit into the branches containing a NOx adsorber-catalyst, and from time-to-time, regenerating the NOx adsorber-catalyst by injecting reductant into the NOx adsorber catalyst's corresponding branch upstream of the NOx adsorber-catalyst; and    (4) method of operating a NOx adsorber-catalyst in the branches of an exhaust after-treatment system comprising allowing a portion of the exhaust to flow into the one branch, adsorbing NOx from the exhaust in the one branch using the NOx-adsorber-catalyst in the one branch during a lean phase, injecting a fuel into the one branch to begin a reformer warming phase, combusting the fuel in the reformer in the one branch to warm the reformer, increasing the fuel flow rate to initiate a rich phase, regenerating the NOx adsorber-catalyst in the one branch, and terminating the fuel flow to begin a new lean phase.    The average proportion of the exhaust flowing into the one branch during the rich phase is greater than or equal to50% of the average proportion of the exhaust flowing into that branch during the lean phase. The exhaust flow is allowed to divide between the branches according to the temperature-dependent friction factors attributable to the fixed geometries of the branches including the devices they contain, the effects of reductant and exhaust flows in the branches, or temperature actuated dampers.    DESCRIPTION OF DRAWING(S) - The figure is a schematic illustration of power generation system.    Power generation system (100)    Exhaust after-treatment system (102)    Branches (111, 114)    Trailing conduit (112)    Fuel injector (121)