Provided are improved exhaust gas cleaning systems and methods for treating exhaust gas from a combustion source that include a hydrogen generation system, a regenerable sulfur oxides trap, and a regenerable nitrogen storage reduction (NSR) catalyst trap. The improved exhaust gas cleaning systems and methods allow for the sulfur released from the sulfur trap to pass through the nitrogen oxide trap with no or little poisoning of NOx storage and reduction sites, which significantly improves NSR catalyst trap lifetime and performance to meet future emissions standards. The disclosed exhaust gas cleaning systems are suitable for use in internal combustion engines (e.g., diesel, gasoline, CNG) which operate with lean air/fuel ratios over most of the operating period.