Process for producing a mixed oxide catalyst, comprising the steps of a) providing a solution and/or suspension of precursor compounds of components of the mixed oxide catalyst, wherein the solution and/or suspension contains precursor compounds of the elements bismuth, molybdenum, iron, cobalt, nickel, manganese, potassium, phosphorous, and samarium, and wherein, if a suspension is subjected to the spray-drying, the concentration of the solids in the suspension is 10 to 50 % by weight, b) spray-drying the solution and/or suspension provided in step a) in co-current together with a gas stream having an entrance temperature into the spray dryer of 160 +/-10°C to 200 +/- 10°C and an exit temperature from the spray dryer of 90 +/- 10°C to 105 +/- 10°C, wherein the gas stream has a mean flow velocity in the spray dryer of 2.0 +/- 0.3 cm/s to 4.5 +/- 0.3 cm/s, or b') spray-drying the solution and/or suspension provided in step a) essentially in co-current together with a main gas stream having an entrance temperature into the spray dryer of 260 +/- 10°C to 300 +/- 10°C and an exit temperature from the spray dryer of 115 +/- 10°C to 130 +/- 10°C, wherein the main gas stream has a mean flow velocity in the spray dryer of 2.0 +/- 0.3 cm/s to 4.5 +/- 0.3 cm/s, with feeding of an additional gas stream having an entrance temperature of not more than 30°C into the spray dryer between the entrance and exit points of the main gas stream into the spray dryer and from the spray dryer, wherein the additional gas stream has a mean flow velocity of less than 2.0 cm/s, and c) calcining the spray particles obtained from step b) or b') to yield a catalytic active mass. a) providing a solution and/or suspension of precursor compounds of components of the mixed oxide catalyst, wherein the solution and/or suspension contains precursor compounds of the elements bismuth, molybdenum, iron, cobalt, nickel, manganese, potassium, phosphorous, and samarium, and wherein, if a suspension is subjected to the spray-drying, the concentration of the solids in the suspension is 10 to 50 % by weight, b) spray-drying the solution and/or suspension provided in step a) in co-current together with a gas stream having an entrance temperature into the spray dryer of 160 +/-10°C to 200 +/- 10°C and an exit temperature from the spray dryer of 90 +/- 10°C to 105 +/- 10°C, wherein the gas stream has a mean flow velocity in the spray dryer of 2.0 +/- 0.3 cm/s to 4.5 +/- 0.3 cm/s, or b') spray-drying the solution and/or suspension provided in step a) essentially in co-current together with a main gas stream having an entrance temperature into the spray dryer of 260 +/- 10°C to 300 +/- 10°C and an exit temperature from the spray dryer of 115 +/- 10°C to 130 +/- 10°C, wherein the main gas stream has a mean flow velocity in the spray dryer of 2.0 +/- 0.3 cm/s to 4.5 +/- 0.3 cm/s, with feeding of an additional gas stream having an entrance temperature of not more than 30°C into the spray dryer between the entrance and exit points of the main gas stream into the spray dryer and from the spray dryer, wherein the additional gas stream has a mean flow velocity of less than 2.0 cm/s, and c) calcining the spray particles obtained from step b) or b') to yield a catalytic active mass.