avoid WAL for refresh of materialized view

Hi all

We have PostgreSql 9.6 running and started to work with materialized views. To refresh the materialized views, we set up a cron job that refreshes the materialized views on a fix schedule.
Since our materialized views cache quite some data, we noticed a considerable increase in WAL files. It seems, that every refresh of a materialized view is logged in the WAL.

We tried to figure out how we can alter the materialized view to set it to "UNLOGGED" but this does not seem possible.
--> "alter materialized view xyz set UNLOGGED;" leads to "ERROR: "xyz" is not a table, SQL state: 42809"

Is there another way to avoid logging a refresh of a materialized view in the WAL?

Kind regards,
Alain Remund