A joint assembly for joining a ceramic membrane of tubular form to a tube sheet used in supporting the ceramic membrane within a reactor. The ceramic membrane is received within a fixture connected to the tube sheet and a follower, extending into the fixture, exerts a force on a high temperature sealing element located between the fixture and the ceramic membrane to effect a seal and to hold the ceramic membrane in place. The force can be exerted directly on the sealing element or on the ceramic membrane itself.