In 8051 9 bit uart mode is used when communicating with multiple devices what is the provision for the same in lpc2148
No, it is not a Keil question!
It is a question about the LPC2148 hardware - and, therefore, a question to which you will find the answer in the LPC2148 documentation.
The capabilities of the LPC2148 (or any other) hardware are not affected by what development tools you use!