A process is disclosed for converting acetic acid to propylene and isobutene as the principal hydrocarbon products made, in the presence of a catalyst and in the further presence of hydrogen. In certain embodiments, a ZnxZryOz mixed oxide catalyst is used for carrying out a gas phase process, and propylene is produced preferentially to isobutene by using at least a certain amount of hydrogen in the process. In some embodiments, a ZnxZryOz mixed oxide catalyst made by an incipient wetness impregnation method is used and is indicated to be very stable for carrying out the conversion.