Effects of varying amounts of Na on Pd/TiO2 for the direct synthesis of H2O2: Identification of the Pd dispersion and catalytic activity enhancement by changing the surface electronic states

•Among the tested catalysts, 0.5 wt.% Na loading (PdNa(0.6)/TiO2) showed the highest Pd dispersion and Pd surface area due to the redispersion of Pd during H2 reduction.•Due to electron donation from Na, the Pd surface electronic states varied, and the H2O2 selectivity of each catalyst varied.•Among the prepared catalysts, PdNa(0.6)/TiO2 exhibited the highest H2 conversion rate (22 %) and H2O2 production rate (600 mmol/gPdh) due to having highest Pd dispersion and surface area in the iso-Pd weight activity tests.•In iso-H2 conversion activity (approx. 12 %) tests, PdNa(0.6)/TiO2 showed the highest H2O2 selectivity (95.4 %) and production rate (785.9 mmol/gPdh) due to its superior suppression ability of H2O2 degradation.