Short answer: Not usually-but there are a few exceptions. Let me explain, 'cause I used to think you needed a special trowel for porcelain (spoiler: I was wrong, most of the time).
First, let's talk about standard ceramic and porcelain tiles. If you're laying 12x12 ceramic tiles (3/8 inch thick) and 12x12 porcelain tiles (same thickness), you can use the same trowel-usually a 1/4x3/8-inch square notch. Porcelain is denser than ceramic, but it doesn't need more thinset-just a good bond. I did a kitchen floor last year: ceramic tiles in the dining area, porcelain in the kitchen, same trowel. Both turned out great-no issues.
Now, the exceptions: Thick porcelain tiles (1/2 inch or more) or large-format porcelain (18x18 or bigger). These need a bigger trowel-like a 1/2-inch square notch-because they're heavier and need more thinset to stay level. I laid 24x24 porcelain tiles (1/2 inch thick) last month, used a 1/2-inch trowel, and they're rock solid. If I'd used a smaller trowel (like the one for standard ceramic), they would've wobbled.
Another exception: Mosaic porcelain tiles. These are small and thin, so you need a 1/4-inch V-notch trowel-same as mosaic ceramic tiles. I did a shower niche with porcelain mosaics once, used a V-notch, and it was perfect.
The bottom line: If the tiles are the same size and thickness, same trowel works. If porcelain is bigger or thicker, bump up the trowel size. Easy peasy.
