Pecan is pretty dense so it will stand up to the elements better than most woods. It will require a good moisture barrier that should be regularly reapplied because water is outdoor wood's biggest weakness and if you use something with a UV protection added that will help.

I wouldn't use Pecan for outdoor furniture. No wood will stand up to the elements in the long term and you'll be doing lots of refinishing which is easier with a less dense wood. I like cedar or a furniture grade pine for outdoor projects. Cedar is exceptional at resisting moisture damage and they are both relatively cheap and easy to sand and refinish. Plus they are lighter and outdoor furniture gets moved around more. I save better woods and especially visually interesting woods like pecan for projects that I will give to someone or that I can pass down.

Edit: somehow moisture became moisturizer in the second sentence, edited to fix that.

Me: imagines very tiny patio furniture carved from nuts

I wouldn’t use it outdoor. It makes a beautiful desk or other indoor furniture