Preheat oven to 350 degrees F (175 degrees C). Line a rimmed baking sheet with aluminum foil. Pour butter over foil layer.
Whisk sugar, egg whites, cinnamon, and cayenne pepper together in a large bowl. Add pecans and toss to fully coat. Spread coated pecans on the buttered baking sheet.
Bake in the preheated oven, stirring and flipping pecans after 10 minutes, until pecans are toasted, about 20 minutes. Cool pecans on baking sheet for 15 minutes.