Process for producing a siliceous ash by the fixing of metals, transition metals and/or oxides thereof on a siliceous support material of vegetable origin, characterized in that: a. a siliceous vegetable biomass containing more than 0.5% of silicates, based on the dry matter of the biomass, is provided, b. the vegetable biomass is impregnated with a solution containing metals and/or transition metals and/or oxides thereof or mixtures thereof, c. the metals and/or transition metals and/or oxides thereof or mixtures thereof present in the vegetable biomass are fixed on the siliceous framework of the vegetable biomass in a combustion step, leaving the siliceous framework on which the metals and/or transition metals and/or oxides thereof or mixtures thereof present have been fixed as ash at the end of the combustion, d. where predrying of the biomass can optionally be carried out before the combustion step c., where the temperature in the combustion step is maintained so that no melts are formed and so that burning out of carbon proceeds to completion, where the temperature range for the combustion in the combustion step is determined as follows in a series of tests: step 1: impregnation of the vegetable biomass with the solution containing the desired metals and/or transition metals and/or oxides thereof or mixtures thereof; step 2: combustion of the impregnated vegetable biomass at a temperature T (lower) for the purpose of burning out carbon, where the temperature T (lower) is the lower limit of the combustion temperature and is postulated to have a value of 200°C; step 3: if burning out of carbon is complete, setting of the temperature T (lower) as lower limit for the combustion temperature, independently of the utilization of the variable T (lower) as auxiliary variable in step 5, and continuation with step 4 if the burning out of carbon is not complete, increasing the temperature T (lower) by 1°C and repetition of step 2; step 4: combustion of the impregnated vegetable biomass at a temperature T (upper), where the temperature T (upper) is the upper limit of the combustion temperature and is postulated to have a value of 2000°C; step 5: if melts are formed in the combustion of step 4, calculation of a new combustion temperature T (upper), where this new combustion temperature is given by the average of T (upper) and T (lower), if no melts are formed in the combustion of step 4, calculation of a new combustion temperature T (upper), where this new combustion temperature is determined by increasing T (lower) and T (upper) by the absolute value of the difference between T (upper) and T (lower) and then forming an average of T (lower) and T (upper); step 6: continuation of step 5 until the temperatures T (upper) and T (lower) differ by less than 0.01°C, where the upper limit for the combustion temperature is set as the value corresponding to T (upper) as obtained from step 5. a. a siliceous vegetable biomass containing more than 0.5% of silicates, based on the dry matter of the biomass, is provided, b. the vegetable biomass is impregnated with a solution containing metals and/or transition metals and/or oxides thereof or mixtures thereof, c. the metals and/or transition metals and/or oxides thereof or mixtures thereof present in the vegetable biomass are fixed on the siliceous framework of the vegetable biomass in a combustion step, leaving the siliceous framework on which the metals and/or transition metals and/or oxides thereof or mixtures thereof present have been fixed as ash at the end of the combustion, d. where predrying of the biomass can optionally be carried out before the combustion step c., step 1: impregnation of the vegetable biomass with the solution containing the desired metals and/or transition metals and/or oxides thereof or mixtures thereof; step 2: combustion of the impregnated vegetable biomass at a temperature T (lower) for the purpose of burning out carbon, where the temperature T (lower) is the lower limit of the combustion temperature and is postulated to have a value of 200°C; step 3: if burning out of carbon is complete, setting of the temperature T (lower) as lower limit for the combustion temperature, independently of the utilization of the variable T (lower) as auxiliary variable in step 5, and continuation with step 4 if the burning out of carbon is not complete, increasing the temperature T (lower) by 1°C and repetition of step 2; step 4: combustion of the impregnated vegetable biomass at a temperature T (upper), where the temperature T (upper) is the upper limit of the combustion temperature and is postulated to have a value of 2000°C; step 5: if melts are formed in the combustion of step 4, calculation of a new combustion temperature T (upper), where this new combustion temperature is given by the average of T (upper) and T (lower), if no melts are formed in the combustion of step 4, calculation of a new combustion temperature T (upper), where this new combustion temperature is determined by increasing T (lower) and T (upper) by the absolute value of the difference between T (upper) and T (lower) and then forming an average of T (lower) and T (upper); step 6: continuation of step 5 until the temperatures T (upper) and T (lower) differ by less than 0.01°C, where the upper limit for the combustion temperature is set as the value corresponding to T (upper) as obtained from step 5.