TOKYO — East Japan Railway Co. is to conduct a test run of the world’s first fuel-cell-powered train in July, the company said Wednesday. The fuel cells, which generate power from a chemical reaction between hydrogen and oxygen, will help reduce environmental pollution compared to the existing electric and diesel engines, the company said. The new power source would also help improve scenery when Japan’s web of railroads drops electric-power lines. The fuel-cell trains will maintain the same current speed at about 100 km per hour, but the railway company is still developing a system capable of long distance travel.