than Tom's/that of Tom

My intelligence is higher than that of Tom.
My intelligence is higher than Tom's.

Are both sentences correct?

To me, both are fine.

Many thanks.

Yes - The second is more usual. The first is awkward and a bit pedantic.

Additionally, the structures here aren't parallel:

1a. My intelligence is higher than that of Tom.
1a. My intelligence is higher than the intelligence of Tom.

Compare:

The climate of Shanghai is milder than that of Tokyo.
The climate of Shanghai is milder the climate of Tokyo.

Thanks for your replies.