Turn on netflow for the Catalyst router:
ip flow-export source (interface name)
ip flow-export version 5
ip flow-export destination (netflow collector IP) (port exported flows go to)
ip flow ingress layer2-switched vlan (any needed vlans)
ip flow-cache timeout active 1
Then configure NetFlow for all the switched traffic:
mls nde sender version 5
mls flow ip interface-full
mls nde interface
mls aging long 64
Finally, configure individual interfaces:
ip route-cache flow
ip flow ingress