I don't want to rain on your parade, you have an interesting idea that frankly I have never seen done (tile on an outdoor deck). However, consider a few things before you go ahead.
Porcelain tile in 24 inch format is considered large format tile. Tile is brittle, and in large format it is more subject to cracking due to load. For such a large format tile, I believe the tile institute recommendation is a stiffness ratio of L720. Normal code deck loading is about 50 pounds per square foot, and you are unlikely to achieve L720 deflection criteria with any reasonable combination of beams and joists. You absolutely need to check the maximum deflection through analysis of your structure, and you are not going to be able to look this up in standard tables, since standard tables are only going to cover 20 psf (attic), 30 psf (bedroom), or 40 psf (kitchen) type loads, and a deck is beyond that loading.
Additionally, your deck is subject to exceptionally harsh temperature swings, which are going to result in unusual stresses on the tile. One of the tile guys here may be able to comment on the effect of 140 degree F temperature swings on tile and grout.
There may be a reason I have never seen a tiled deck, and it probably relates to deflection and temperature swings. But maybe one of our tile pros knows how to do it so you won't have any problems.