Abstract: A composition is provided for neutralizing acid corrosive agents in boiler flue gases and like vapors. In large industrial boilers and like systems, flue gases carrying sulfur trioxide contact metal surfaces of heat recovery equipment. Under some circumstances, the sulfur trioxide combines with moisture in the boiler flue gases to produce sulfuric acid. This acid can corrode the surfaces of this equipment. The composition offered here comprises a particulate carrier having a relatively large surface area, and a particulate, active neutralizing agent having a relatively small surface area surface-coated on the carrier. Here, the particulate carrier is bentonite clay and the active neutralizing agent is sodium aluminate.