In the title compound, (5-oxo-3a,6a-diphenylperhydroimidazo[4,5-d]imidazol-2-ylidene)oxonium hydrogen sulfate, C16H15N4O2+ x HSO4-, the asymmetric unit contains a hydrogen sulfate anion and a 3a,6a-diphenylglycoluril oxonium cation. The hydrogen sulfate anion is joined to the oxonium cation via a strong O-H...O hydrogen bond (H...O = 1.69 A). The crystal packing is mainly dominated by interactions involving the hydrogen sulfate anion. The diphenylglycoluril oxonium cations also self-assemble through N-H...O hydrogen bonds, forming molecular chains along the [001] vector. Four intramolecular C-H...N hydrogen bonds are observed, having an S(5) motif.

The two title chromene compounds, 3,3a-dihydrocyclopenta[b]chromen-1(2H)-one, C16H12O2, (I), and 2-(2-hydroxybenzylidene)-3,3a-dihydrocyclopenta[b]chromen-1(2H)-one, C19H14O3, (II), have been determined in the monoclinic space group P2(1)/n. Compound (I) is mainly stabilized by C-H...pi interactions. Compound (II) is linked into infinite one-dimensional chains with a C(3) motif via intermolecular O-H...O hydrogen bonds. The intermolecular C-H...pi and pi-pi interactions also play key roles in stabilizing the crystal packing. Two intramolecular C-H...O hydrogen bonds with S(5) motifs were detected in (II).

Manganese oxides supported palygorskite (MnOx/PG) catalysts used for low-temperature selective catalytic reduction of NO with NH3was modified by doping cerium oxide as additive for enhancement of its performance. The effects of doped cerium content on catalysts' activity were investigated. It was found that the NO removal efficiency of Mn8Ce5/PG catalyst was remarkably higher than Mn8/PG catalyst especially at low temperatures, revealing that the addition of cerium oxide effectively enhanced the catalysts' SCR activity. Catalysts were characterized by BET, XRD, XPS to explore the relation between structural properties and increasing in SCR activity via modification. Results showed that the doping of cerium oxide has improved the dispersion of manganese oxides as active species. And furthermore, the stability of surface MnO2was also improved which was suggested to be the main reason for the enhancement of catalysts' activity.