Here is the most complete description of the reaction that I’ve found. Yes, ammonia (NH3) is the end result. First, hydrogen is derived from natural gas by another process (described in the linked article). The hydrogen is then combined with nitrogen (N2, from air) under great pressure (100–250 atmospheres). A very small amount of ammonia would result from this combination under pressure alone, but the efficiency of the reaction is increased enormously by the presence of a catalyst in the reaction chamber. Various metals can be used as catalysts for this reaction, but the cheapest and most commonly used is magnetite (an iron oxide) with minor amounts of calcium and aluminum oxides. The catalyst forms intermediate reactions with the nitrogen and hydrogen which allows them to combine with less total energy than they would need to combine directly.