In Spain we don't have so many surnames prefixed with particles, but we do have some (e.g. "Del Río") and the capitalization also works as you describe for Dutc

In Spain we don't have so many surnames prefixed with particles, but we do have some (e.g. "Del Río") and the capitalization also works as you describe for Dutch. It makes sense: when you say Juan del Río it's obvious that it's a surname, but if you just said "del Río" without context, the "del" could be confused with the common word.