Effect of different sulfides on the sulfur modification properties of active r-Al2O3 carriers
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I would like to ask everyone: Recently, I have seen studies in which aqueous solutions of ammonium sulfide and ammonium sulfate were used to carry out sulfur modification on the active alumina carrier r-Al2O3 used for preparing catalysts. After impregnating the aforementioned sulfide, it is dried and then calcined. r-Al2O3 carriers capable of \"resisting sulfur poisoning\" can be obtained, which are then impregnated with Pt, Pd, and other noble metal active components using a partially modified carrier. Thus, \"sulfur-resistant precious metal deoxidizers\" and \"dehydrogenators\" that can be used for gas deoxidation, dehydrogenation, etc., can be obtained. Capable of dealing with trace amounts of sulfur-containing toxins such as COS and H2S present in gases. It has a longer service life than conventional gas deoxidizers and dehydrogenators prepared by loading Pt and Pd on r-Al2O3 carriers that have not been sulfur-modified. But one thing is unclear: what is the difference between modifying the carrier with ammonium sulfide (NH4)2S and ammonium sulfate (NH4)2SO4? Which has a better effect on modifying r-Al2O3 carriers with the two sulfur-containing substances? Is there any theoretical basis? I only know that the valence of sulfur in these two sulfides is different; one has a valence of -2, while the other has a valence of +6. Those who know the principle please explain it to me; thank you!
The main difference in modifying the active alumina r-Al2O3 carrier using ammonium sulfide (NH4)2S and ammonium sulfate (NH4)2SO4 lies in the different oxidation states of sulfur in these two sulfides, which in turn affects the distribution and chemical state of sulfur on the carrier, and further influences the carrier’s resistance to sulfur as well as its ability to support precious metals. 1. In ammonium sulfide ((NH4)2S), sulfur is in the -2 valence state and can directly react with or deposit on the surface of activated alumina in the form of sulfides. This approach may enable sulfur to be distributed more evenly on the surface of the carrier, forming more stable sulfide species that help resist sulfur poisoning and improve the overall performance of the carrier. 2. In ammonium sulfate (NH4)2SO4, sulfur is in the +6 valence state; its modification process may involve more complex reduction steps to convert sulfate ions into lower-valent sulfur or sulfides with higher reactivity. The effect of ammonium sulfate modification may be more influenced by heat treatment conditions (such as the temperature and environment during calcination), as the reduction process of sulfate ions requires suitable conditions to proceed. Theoretically, since the -2 valent sulfur provided by (NH4)2S directly participates in the reaction, it may be easier to control the chemical state and distribution of sulfur on the carrier, thereby more effectively improving the sulfur resistance of the catalyst. On the other hand, (NH4)2SO4 modification may require stricter treatment conditions to ensure effective conversion and distribution of sulfur. Overall, the (NH4)2S-modified r-Al2O3 carrier may be more effective in improving sulfur resistance, though the specific effects still need to be further verified through experimental data. These differences ultimately affect the performance and lifespan of the active precious metal components such as Pt and Pd loaded therein. .