A process for commencing a continuous reaction in a reactor system includes introducing a catalyst to a catalyst processing portion of the reactor system, the catalyst initially having a first temperature of 500 C or less, and contacting the catalyst at the first temperature with a commencement fuel gas stream, which includes at least 80 mol % commencement fuel gas, in the catalyst processing portion. Contacting of the catalyst with the commencement fuel gas stream causes combustion of the commencement fuel gas. The process includes maintaining the contacting of the catalyst with the commencement fuel gas stream until the temperature of the catalyst increases from the first temperature to a second temperature at which combustion of a regenerator fuel source maintains an operating temperature range in the catalyst processing portion.