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The fluidization of TiO2-P25 nanoparticles is characterized by studying the X-ray attenuation through the bed and the dynamic response of pressure fluctuations to the influence of the gas velocity. The X-ray results are based on a flat detector capable of measuring a 2D projection of the column from a height of 3 cm above the distributor to the freeboard. Pressure fluctuation signals are analyzed in the time and frequency domain. The strong influence of hysteresis when increasing or decreasing the gas flow is used in the experiments to compare a well fluidized state to channels formation. Thus, two experimental procedures were carried out changing the gas velocity. First, the gas flow is decreased changing from fully fluidized to packed bed. In the second type of tests, the gas velocity is increased from packed bed to well fluidized. The use of Digital Image Analysis (DIA) techniques to study the Xray images show the homogeneous distribution of solids within the bed when the gas velocity is decreased. In these tests, a smooth fluidization is found up to a gas velocity of 3 cm/s, while higher gas flows change the bed state to vigorous fluidization. Pressure signals revealed that Baskakov's frequency can be used to determine the regime of the bed, smooth or vigorous bubbling. Tests with poor fluidization show that the formation of channels modifies the bed structure, hindering to reach the fluidization quality of well fluidized tests for the same experimental conditions. (C) 2016 Elsevier B.V. All rights reserved.