An alumina catalyst containing, expressed as the oxide content by weight, at least 50% Al2O3, 2-10% by weight of cobalt oxide CoO, 10-30% by weight of molybdenum oxide MoO3 and 4-10% of phosphorous oxide P2O5, with a BET surface area in the range 100-300 m2/g, a crushing strength CSH of more than 1.4 MPa, and an average pore diameter in the range 8-11 nm, and based on the total pore volume, the pore volume of pores with a diameter of more than 14 nm being less than 22%, the volume of pores with a diameter of less than 8 nm being less than 10%, the volume of pores with diameter less than 10 nm being in the range of 20%-70%, the volume of pores with diameter between 10 nm and 13 nm being in the range of 20%-60%, the volume of pores with a diameter which is in the range 8 to 14 nm being in the range 0.20 ml/g to 0.8 ml/g, with less than 0.08 ml/g having a pore size of greater than 140 Å, and with less than 10% of the pore volume having a pore size above 250 Å.