First, the relevant verse in yours and my discussion is Rom 9:14~~
New International Version
What then shall we say? Is God unjust? Not at all!
New Living Translation
Are we saying, then, that God was unfair? Of course not!
English Standard Version
What shall we say then? Is there injustice on God’s part? By no means!
New American Standard Bible
What shall we say then? There is no injustice with God, is there? May it never be!
King James Bible
What shall we say then?
Is there unrighteousness with God? God forbid.
So , Yes God can prepare a vessel for wrath. His Justice demands wrath for anyone that does not believe and He has Righteous norms and standards that He will follow For the unbeliever. I believe that you are confusing "create" a vessel for wrath and "prepare" a vessel for wrath.
If He "Created" a vessel for wrath and "created" another vessel for mercy Rom 9:14 would not have been written in His Word.
That lump of clay is actually our freewill. And He has every right to "prepare" us the way He sees fit according to the way we use our freewill,And according to the norms and standards that His Sovereignty established.
20 Now in a large house there are not only gold and silver vessels, but also vessels of wood and of earthenware, and some to honor and some to dishonor.
21 Therefore,
if anyone cleanses himself from these things, he will be a vessel for honor, sanctified, useful to the Master, prepared for every good work.
"Cleanses"~~
ekkaqairw 1571 aor act sub 3s ---verb purge 4
Cleanses is in the active voice. Which expresses that the subject is choosing.