No abstract

Ethane turnovers to ethylene in either oxidehydrogenation with diverse oxidants (O 2 , CO 2 , H 2 O) or dehydrogenation (without an oxidant) over two-dimensional MoO x dispersed on Al 2 O 3 catalyst occur via a generalized mechanistic framework encompassing ternary catalytic cycles of C 2 H 6 activation, oxidant activation, and carbon removal. This is confirmed from rate assessments, detailed kinetic analysis accounting for active site loss, isotopic tracer studies, and detailed spectroscopic characterization. Irrespective of the oxidant's chemical identity, the C 2 H 6 activation cycle occurs via the kinetically relevant C−H bond activation of C 2 H 6 on lattice oxygen of MoO x , forming C 2 H 4 . The concomitant oxidant activation cycle either replenishes the oxygen vacancies or generates reactive oxygen species, which scavenge unwanted carbonaceous debris deposited on catalyst surfaces at contents dictated by the chemical identity of the oxidant and oxygen chemical potential that it exerts. Among the oxidants, O 2 is the most effective, as it removes coke effectively, leading to essentially no rate decay. CO 2 and H 2 O are alternate soft oxidants, and their use prevents the overoxidation of ethylene, thus resulting in higher ethylene selectivity (80−85%) than using O 2 . CO 2 activation is, however, severely restricted kinetically, as evidenced from the reverse water−gas shift reaction that is far away from chemical equilibrium; thus, the generation of reactive oxygen species and their ability to concomitantly oxidize coke are much less effective than those with O 2 oxidant. H 2 O dissociation is rapid and quasi-equilibrated, but its activation converts a portion of the active lattice oxygen to hydroxy species, reducing the active oxygen centers and lowering C 2 H 6 turnovers. The rates of the C 2 H 6 activation cycle dictate the intrinsic rates, whereas those of the concomitant oxidant activation and carbon removal cycles dictate the surface lattice oxygen density available for catalysis and in turn the extent of rate decay. Consolidating these findings within a generalized mechanistic framework leads to a universal rate expression containing two terms, one accounting for an intrinsic C 2 H 6 activation rate and a second one for the time-dependent rate decay. This universal rate expression captures the kinetic properties of early transition-metal oxides in C 2 H 6 catalysis, irrespective of the chemical identity of the oxidant.

Background. Regulatory B cells (Breg) are a distinct B cell subset with immunoregulatory properties. Pivotal to Breg function is interleukin-10. This study was to investigate the role of IL-10-producing B cell (B10) and its association with Treg and Th17 subsets in immune thrombocytopenia (ITP) patients. Methods. Peripheral blood mononuclear cells from ITP patients and controls were stimulated with PMA, ionomycin, and Brefeldin A. The frequencies of CD19+IL-10+ B cells, CD3+CD4+IL-17+ Th17 cells, and CD4+CD25hiFoxp3+ Treg cells were analyzed by flow cytometry. The mRNA expression of Foxp3 and RORγt was detected by real-time quantitative PCR. Results. The number of B10 cells was elevated in ITP patients. After first-line therapies, it remained at high level in patients who achieved complete or partial response but decreased in those who acquired no response. There was a positive correlation between B10 cells and Tregs in ITP both before and after therapies. The ratio of Treg/Th17 decreased in ITP, and it strongly correlated with B10 cells. Conclusions. The frequency of B10 cells is elevated in ITP and it correlates with both the Tregs counts and the Treg/Th17 ratio. B10 cells to regulate functional T cell subsets might be impaired in patients with ITP.