I think that the Berlin Wall is not as much a catalyst to the Cold War as a reflection of it.  When I consider the role of a "catalyst," what comes to my mind is something that initiated the event.  I don't see this description in the Berlin Wall.  I think that the construction of the Berlin Wall was a reflection of political reality and mistrust between both the Soviets and the Western side of the wall.  The growing chasm between both sides and both visions of political reality is what enables the Berlin Wall to emerge.  The construction of the wall is a reflection of the mistrust between both sides.  For the West, there was a sincere fear/ misunderstanding of the Soviet Union, who, for their part, displayed a complete lack of trust in the same forces that helped it defeat Hitler and the Nazis.  The Berlin Wall is a reflection of this antagonism, and not necessarily a catalyst of it.  Those tensions had been present and the wall was more of an embodiment of it.  I do not see the building of the Berlin Wall as an initiating agent of the Cold War, rather a mirror of it.