NOVELTY - Preparing catalyst comprises e.g. pouring titanium tetrachloride solution in beaker, placing in ice water environment, using UV rays for irradiation, and quickly stirring, slowly adding deionized water into the beaker, using titanium tetrachloride for hydrolysis reaction, and adding sodium dodecylbenzenesulfonate, regulating liquid pH value, and aging, subjecting the resulting turbid liquid to suction filtration, taking the resulting solid and drying, calcining, removing the solid, cooling, and grinding into granules, and spreading the granules and dry ice in a quartz glass.    USE - The catalyst is useful for reducing concentration of carbon dioxide (claimed).    ADVANTAGE - The catalyst: has high stability; solves the problems of the existing catalyst having high energy consumption and low reactant conversion rate; has high carbon dioxide conversion efficiency; and can reduce the concentration of carbon dioxide to 200 mg/m3 or less in air.    DETAILED DESCRIPTION - Preparing catalyst comprises (i) taking 10-18 ml titanium tetrachloride solution, pouring in 200 ml beaker, placing in ice water environment, using UV rays for irradiation, and quickly stirring, (ii) taking 30-50 ml deionized water, slowly adding into the beaker, controlling temperature at 28-35 degrees C, using titanium tetrachloride for hydrolysis reaction, then adding 3-5 g sodium dodecylbenzenesulfonate, (iii) using aqueous ammonia for regulating liquid pH value to 6-7, and aging for 8-10 hours, (iv) subjecting the resulting turbid liquid to suction filtration, taking the resulting solid and placing in a drying box and drying at temperature of 110 degrees C, then placing in a calcining furnace for calcining at temperature of 600-700 degrees C, preserving heat for 2-3 hours, removing the solid from the calcining furnace, cooling to room temperature, and grinding into granules of 5-10 mm, (v) uniformly spreading the granules and 10-25 g dry ice in a quartz glass, pushing into a reaction furnace with then constant temperature area, increasing the temperature of the reaction furnace to 500-600 degrees C, and maintaining the temperature for 8 hours, (vi) removing residual air within quartz glass using nitrogen, introducing methane and cold hydrogen, and cooling the quartz glass to room temperature, and (vii) taking out the quartz boat, pouring the particles of the quartz glass into 20% hydrochloric acid solution to soak for 5 hours, maintaining temperature for 60 degrees C, then filtering, using deionized water for washing, and drying.