欢迎您到北京来欢迎您"到"(arrive)北京"来"(come). = 欢迎您来到北京欢迎您"来到"(to come to and arrive in)北京. - Welcome you to come to (and arrive in) Bejing.
The above sentence is the more formal way of greeting. Less formally, you can say:
欢迎您到北京 - Welcome you to arrive in Bejing.
欢迎您来北京 - Welcome you to come to Bejing.