Methods of preparing an acidic catalyst are disclosed that include heating a metal halide to produce a vapor phase metal halide, contacting an initial support material with the vapor phase metal halide in a reaction vessel causing a first chemical reaction and producing an intermediate acidic catalyst, contacting the intermediate acidic catalyst with HBr causing a second chemical reaction and producing an acidic catalyst product which is both more acidic than the intermediate acidic catalyst and more acidic than the initial support material.