The effect of sulfur and phosphorus compounds on supported platinum catalyst activity

The effect of sulfur poisoning on the activity of catalysts containing 1.5% platinum supported on {dollar}gamma{dollar}-{dollar}rm Alsb2 Osb3, TiOsb2, ZrOsb2, or SiOsb2{dollar} was investigated in this study. These four catalysts were aged with 100 ppmv H{dollar}sb2{dollar}S in air at 400'C for 24 hours to determine the effect of sulfur poisoning under oxidizing conditions. In separate experiments, 1.5% Pt/{dollar}gamma{dollar}-{dollar}rm Alsb2 Osb3{dollar} catalyst was aged in nitrogen containing 100 ppmv H{dollar}sb2{dollar}S to obtain a frame of reference for non-oxidizing conditions.; The oxidation of 1% CO, 1% methane, and 1% propane was used with both fresh and aged catalysts as diagnostic reactions to evaluate catalyst activity changes. Catalyst characteristics of both fresh and aged catalysts were determined to obtain possible deactivation pathways.; It was found that all aged catalysts were deactivated for both CO and methane oxidation, and promoted for propane oxidation except for 1.5% Pt/SiO{dollar}sb2{dollar} catalyst. Catalyst characterization studies suggest that the enhancement of activity for propane oxidation is due to the formation of sulfate on the {dollar}gamma{dollar}-{dollar}rm Alsb2 Osb3, TiOsb2, and ZrOsb2{dollar} supports. The decrease in activity for CO oxidation is due to strong adsorption of sulfur compounds (SO{dollar}rmsb{lcub}x{rcub}{dollar}) on the Pt active sites which inhibited CO adsorption. Both sulfur effects, i.e., sulfate formation and strong adsorption of sulfur compound on Pt active sites, deactivate catalyst for methane oxidation. The activity loss for CO oxidation was greater than that for methane oxidation.; It was found that 1.5% Pt/{dollar}gamma{dollar}-{dollar}rm Alsb2 Osb3{dollar} catalysts aged with H{dollar}sb2{dollar}S in air and nitrogen could be regenerated by hydrogen treatment at 350{dollar}spcirc{dollar}C. After regeneration, CO and propane diagnostic oxidation tests showed that activity of catalyst aged in nitrogen for both CO and propane oxidation can partially recover fresh catalyst activity. However, catalyst aged in air can partially recover its activity only for CO oxidation. This suggests that catalyst once poisoned by sulfur to form sulfate on the support, will permanently maintain the enhanced activity for propane oxidation, even after sulfur has been partially removed. The effect of increased dose of sulfur on the enhancement of activity for propane oxidation was not investigated, nor were lifetime effects.; Phosphorus poisoning effects on supported platinum catalyst due to tributyl phosphate (TBP) was also studied. Catalyst containing 0.05 gram 1.5% Pt/{dollar}gamma{dollar}-{dollar}rm Alsb2 Osb3{dollar} were poisoned by 1 cm{dollar}sp3{dollar} TBP in air at both 400 and 550{dollar}spcirc{dollar}C, respectively. Diagnostic oxidation of CO, methane, and propane with fresh and poisoned catalysts showed that catalyst poisoned at 400{dollar}spcirc{dollar}C were slightly deactivated due to the formation of {dollar}rm Psb2 Osb5{dollar} which deposited on catalyst surface and blocked the pore entrance. Catalyst poisoned by TBP at 550{dollar}spcirc{dollar}C were irreversibly deactivated. At the higher temperature, not only did the activity for methane oxidation decrease, but selectivity to CO{dollar}sb2{dollar} decreased producing predominately CO. It is believed that this effect is due to the modification of Pt sites with the phosphorus compounds and the formation of Al PO{dollar}sb4{dollar} on the catalyst surface.