 In 1968, a rhodium-based catalyst ("cis"−[Rh(CO)2I2]−) was discovered that could operate efficiently at lower pressure with almost no by-products.US chemical company Monsanto Company built the first plant using this catalyst in 1970, and rhodium-catalyzed methanol carbonylation became the dominant method of acetic acid production (see Monsanto process).In the late 1990s, the chemicals company BP Chemicals commercialised the Cativa catalyst ([Ir(CO)2I2]−), which is promoted by iridium for greater efficiency.