Translation:Is the restaurant close to the train station?
Del: "de + el" would be "del". "From the", "of the", or "by the", masculine, will be "del". If it's feminine, it will be "a la", which will not combine.
Also, if you're saying "to the" or "at the" you get "a+el" which will give you "al", not to be confused with "a+la".
Grammatically correct, you will never say "de el" or "a el".
"Cerca de" means near and you will often find it in a list of prepositions. You have apparently studied other languages and therefore you have probably found many idiomatic expressions that are commonly used. In Spanish "cerca de" is one of those idiomatic expressions. Searches for reasons for this can take you on a convoluted search that will certainly drive you crazy. In my language studies in the past 60 years I have learned the frustration of trying to rationalize such expressions.