The　effect　of　nickel　additive　on　Pd/TiO2　catalyst　for　selective　catalytic　reduction　of　NO　with　H2　in　presence　of　O2　was　investigated.　Synergistic　effects　between　palladium　and　nickel　were　found　on　the　catalytic　activity　and　N2　selectivity　for　the　H2-SCR　reaction.　Hydrogen　adsorption　isotherm　and　transient　reaction　experiment　results　showed　that　the　nickel　additive　enhanced　the　distance　and　rate　of　hydrogen　spillover.　Operando　diffuse　reflectance　infrared　spectroscopy　(DRIFTS)　with　transient　experiments　indicated　that　addition　of　nickel　to　Pd/TiO2　led　to　the　formation　of　extra　active　monodentate　nitrates,　and　enhanced　the　activities　of　the　bidentate　nitrates.　These　positive　effects　on　the　formation　of　spiltover　hydrogen　and　active　adsorbed　NOx　species　led　to　the　promotional　effect　on　the　extra　reaction　intermediate　NHx　species,　which　was　crucial　for　the　enhancement　of　H2-SCR　activity.　All　these　results,　from　a　view　of　reaction　mechanism,　provided　a　promising　way　for　rational　preparation　of　high-performance　H2-SCR　catalysts.　©　2019　Elsevier　Inc.