Exhaust gas aftertreatment systems play a key role in controlling transportation greenhouse gas emissions. Modern aftertreatment systems, often based on Pd metal supported on aluminum oxide, provide high catalytic activity but are vulnerable to sulfur poisoning due to formation of inactive sulfate species. This paper focuses on regeneration of Pd-based catalyst via the decomposition of alumina-supported aluminum and palladium sulfates existing both individually and in combination. Decomposition experiments were carried out under hydrogen (10% H2/Ar), helium (He), low oxygen (0.1% O2/He), and excess oxygen (10% O2/He). The structure and composition of the model catalysts were examined before and after the decomposition reactions via powder X-ray diffraction and elemental sulfur analysis. The study revealed that individual alumina-supported aluminum sulfate decomposed at a higher temperature compared to individual alumina-supported palladium sulfate. The simultaneous presence of aluminum and palladium sulfates on the alumina support decreased their decomposition temperatures and led to a higher amount of metallic palladium than in the corresponding case of individual supported palladium sulfate. From a fundamental point of view, the lowest decomposition temperature was achieved in the presence of hydrogen gas, which is the optimal decomposition atmosphere among the studied conditions. In summary, aluminum sulfate has a two-fold role in the regeneration of a catalyst—it decreases the Pd sulfate decomposition temperature and hinders re-oxidation of less-active metallic palladium to active palladium oxide.

In this study, the structure of methoxymagnesium chloride (MgCl(OMe)) and its interaction with ester electron donors (diisobutyl phthalate and ethyl benzoate) and TiCl 4 were studied using experimental (PXRD, DRIFT, CP/ MAS 13 C NMR) and computational (DFT; M06-2X functional) methods. Alkoxymagnesium chlorides (MgCl(OR)) have been claimed in several patents to be potential support materials for Ziegler−Natta catalysts. We have found that MgCl(OMe) possesses a layered structure similar to that of MgCl 2 . An energy comparison among MgCl 2 , Mg(OMe) 2 , and MgCl(OMe) structures indicates that mixing of Cl and OMe, and thus the formation of methoxymagnesium chloride, is thermodynamically feasible. Computational results suggest an energetic preference for MgCl(OMe) being structurally composed of MgCl 2 and Mg(OMe) 2 units, which are arranged in a form of alternating stripes. Based on both spectroscopic and computational data, the coordination of ester electron donors on MgCl(OMe) is much weaker than on MgCl 2 . On the other hand, the coordination of TiCl 4 is stronger in the case of MgCl(OMe). TiCl 4 prefers to coordinate on the (110)-like surface of MgCl(OMe), whereas ester electron donors exhibit no particular preference for either the (110)-like or (104)-like surfaces. MgCl(OMe)/TiCl 4 product was found to be an active catalyst in ethylene polymerization.

Decomposition of PdSO4, a species responsible for the deactivation of Pd-based methane combustion catalysts, was studied using a PdSO4/Al2O3 model system. PdSO4 was observed to behave differently under different reaction conditions. The decomposition of PdSO4 under inert atmosphere probably involved only one reaction step and resulted in the formation of metallic palladium. Under H2-containing atmosphere, the decomposition of PdSO4 resulted eventually in the formation of Pd4S, which is probably one of the many possible sulfur-containing palladium species that can be formed during regeneration of a sulfur-poisoned Pd-rich methane combustion catalyst. The formation of Pd4S can provide a reasonable explanation to the threshold temperature of sulfur removal from the catalyst, as well as to the residual sulfur present in the catalyst after regeneration under reductive atmosphere. Overall, the results obtained in the study provide deeper insight into the regeneration process of Pd-based catalysts, possibly enabling development of a more efficient regeneration strategy.

In this study, crystalline magnesium chloride-electron donor complexes were prepared by recrystallization of δ-MgCl in the presence of chelating electron donors, including two diethers (1,2-dimethoxyethane; DME and 1,3-dimethoxypropane; DMP) and one diamine (N,N'-diethylethylenediamine; DEEDA). The syntheses and crystal structures of such magnesium chloride complexes with chelating ligands have been rarely reported, even though they can provide important information for the selection of electron donors for stereoselective MgCl-supported Ziegler-Natta catalysts. The synthesized complexes were characterized using single-crystal X-ray diffraction, and FTIR and CP/MAS C NMR spectroscopy methods. A polymeric complex [MgCl(DME)] and molecular complexes [MgCl(DMP)(HO)] and [MgCl(DEEDA)] were formed in recrystallizations. In all complexes, the bidentate electron donors are bound in chelate binding mode. The [MgCl(DME)] complex, the structure of which consists of a helical polymeric MgCl backbone chain and one DME molecule coordinated to each Mg atom, can be considered as a structural model for layered MgCl. The crystal structure of the [MgCl(DMP)(HO)] complex is composed of a tetrahedral Mg atom with four Cl ligands and a distorted octahedral Mg atom with two DMP molecules, one water molecule, and one Cl ligand. The two types of Mg atoms are connected to each other with a bridging Cl ligand. In the [MgCl(DEEDA)] complex, magnesium is octahedrally coordinated by two chloride ligands trans to each other and two DEEDA molecules. The structures of the obtained magnesium chloride-electron donor complexes clearly show how diether and diamine electron donors can dictate the crystal structure of MgCl.