20 research outputs found
Reaction Mechanism of Aromatic Ring Amination of Benzene and Substituted Benzenes by Aqueous Ammonia over Platinum-Loaded Titanium Oxide Photocatalyst
The
reaction mechanism of photocatalytic aromatic ring amination
of benzene and the derivatives with aqueous ammonia was clarified
by some reaction experiments and electron spin resonance spectroscopy
as follows: a platinum-loaded titanium oxide photocatalyst oxidizes
an ammonia to form an amide radical (·NH<sub>2</sub>) and a proton,
and the amide radical attacks an aromatic ring to produce an intermediate,
followed by the abstraction of the hydrogen atom from it on the platinum
sites to produce an aniline. Simultaneously, the photocatalyst also
promotes the reduction of a proton to form a hydrogen radical on the
platinum sites, and it reacts with the abstracted hydrogen to produce
a molecular hydrogen. The photocatalytic aromatic ring amination proceeded
for many kinds of monosubstituted benzenes except for phenol, and
high selectivity was recorded for benzonitrile and halogenated benzenes.
It is noted that the distributions of the aminated isomers were unique,
i.e., the <i>para-</i>isomer was predominantly produced
in the case of nitrobenzene, and <i>ortho-</i>isomers were
preferentially produced in the case of the other substrates, which
would depend on the approaching direction of the molecule to the photocatalyst
surface
Bifunctional Rhodium Cocatalysts for Photocatalytic Steam Reforming of Methane over Alkaline Titanate
Photocatalytic steam reforming of methane (PSRM; 2 H<sub>2</sub>O (g) + CH<sub>4</sub> → 4 H<sub>2</sub> + CO<sub>2</sub>)
was examined over metal-loaded K<sub>2</sub>Ti<sub>6</sub>O<sub>13</sub> photocatalysts. Although the production rate was improved by loading
Pt cocatalyst on the K<sub>2</sub>Ti<sub>6</sub>O<sub>13</sub> photocatalyst,
unfavorable formation of CO and gradual deactivation of photocatalyst
were observed. On the other hand, a Rh-loaded K<sub>2</sub>Ti<sub>6</sub>O<sub>13</sub> sample showed two times higher activity than
the Pt-loaded one did, and promoted the PSRM selectively without deactivation
for many hours. In the highly active Rh-loaded photocatalyst, the
Rh cocatalyst existed as a mixture of small metallic rhodium and large
rhodium oxide particles. The photocatalytic activity tests for hydrogen
evolution and oxygen evolution from each aqueous solution of sacrificial
reagent (methanol and silver nitrate, respectively) revealed that
the metallic rhodium particles and the rhodium oxide particles could
function as cocatalysts preferably for reduction and oxidation, respectively.
Also on a Na<sub>2</sub>Ti<sub>6</sub>O<sub>13</sub> photocatalyst,
a mixture of rhodium metal and oxide similarly enhanced the photocatalytic
activity. Thus, it is suggested that the Rh cocatalyst on these alkaline
titanates bifunctionally promoted the PSRM
Reaction Mechanism of Aromatic Ring Hydroxylation by Water over Platinum-Loaded Titanium Oxide Photocatalyst
Direct aromatic ring hydroxylation of benzene derivatives
by using water as an oxidant over platinum-loaded titanium oxide photocatalyst
proceeded with high selectivity under the light of selected wavelength.
Two kinds of electrophilic active species, which depended on the reaction
condition, were proposed: a surface oxygen radical in neutral or acidic
conditions and a hydroxyl radical in basic condition, both of which
were produced by a photoformed hole on the surface of titanium oxide.
In both cases, these active species can attack the aromatic ring to
form an intermediate, followed by the formation of a hydroxylated
product. Thus, the reaction proceeds through the addition–elimination
mechanism. On the other hand, a photoformed electron reduces a proton to form
a hydrogen radical, which reacts with the intermediate to produce
a hydroxylated product and a molecular hydrogen or with another hydrogen
radical to form a molecular hydrogen
Sites et monuments : bulletin de la Société pour la protection des paysages et de l'esthétique générale de la France
juillet 19841984/07 (N106)-1984/09
Additional file 2: of Available, Bed-sided, Comprehensive (ABC) score to a diagnosis of Methicillin-resistant Staphylococcus aureus infection: a derivation and validation study
Comparison of the two patient cohorts. (PDF 149 kb
Structural Characterization of 2D Zirconomolybdate by Atomic Scale HAADF-STEM and XANES and Its Highly Stable Electrochemical Properties as a Li Battery Cathode
The
structural determination of nanomaterials and their application in
energy storage and transfer are of great importance. Herein, a layered
zirconomolybdate with a two-dimensional structure was synthesized.
Atomic resolution electron microscopy was utilized for direct visualization
of the structure that was further confirmed by powder X-ray diffraction
and X-ray absorption near-edge structure analyses. The structure of
the molecular sheet was stable at a high temperature in an oxidative
atmosphere. The electrochemical performance of the material was evaluated
with a Li battery composed of the calcined material as a cathode.
Li ions were reversibly inserted and extracted between the layers
without collapse of the structure of the material. The electrochemical
properties of the material were derived from the reversible redox
activity of the Mo ions and Zr ions in the material as well as the
flexibility of the molecular layer of the material
Durability of immunity by hepatitis B vaccine in Japanese health care workers depends on primary response titers and durations
<div><p>Background</p><p>Health care workers (HCWs) are frequently exposed to hepatitis B virus (HBV) infection. The efficacy and safety of immunization with the hepatitis B (HB) vaccine are well recognized, but the durability of immunity and need for booster doses in those with secondary vaccine response failure remains controversial.</p><p>Methods</p><p>This was a retrospective cohort study performed at Osaka University Hospital, Japan. We examined antibodies against HB surface antigen (anti-HBs) titers annually after immunization for previously non-immunized HCWs. Primary responders were categorized by their sero-positive durations as short responders (those whose anti-HBs titers declined to negative range within 3 years), and long responders (those who retained positive anti-HBs levels for 3 years and more). We re-immunized short responders with either single or 3-dose boosters, the long responders with a single booster when their titers dropped below protective levels, and examined their sero-protection rates over time thereafter.</p><p>Results</p><p>From 2001 to 2012, data of 264 HCWs with a median age of 25.3 were collected. The rate of anti-HBs positivity after primary vaccination were 93.0% after three doses (n = 229), 54.5% after two doses (n = 11), and 4.2% after a single dose (n = 24). Of 213 primary responders, the anti-HBs levels of 95 participants (44.6%) fell below the protective levels, including 46 short responders and 49 long responders. HCWs with higher initial anti-HBs titers after primary vaccination had significantly longer durations of sero-positivity. For short responders, 3-dose booster vaccination induced a longer duration of anti-HBs positivity compared to a single-dose booster, whereas for long responders, a single-dose booster alone could induce prolonged anti-HBs positivity.</p><p>Conclusion</p><p>Our preliminary data suggested that it may be useful to differentiate HB vaccine responders based on their primary response durations to maintain protective levels of anti-HBs efficiently. A randomized, prospective, large-scale study is warranted to support our findings.</p></div
Initial anti-HBs titers of primary responders after full series of vaccination and its duration of positivity.
<p>(A) A box indicates a median and interquartile range, and error bars denote the 10th and 90th percentiles. (B) High (> 500 mIU/mL, n = 35), moderate (100–500 mIU/mL, n = 62), and low (< 100 mIU/mL, n = 46) titers. It was a significant trend that individuals with lower titers of initial anti-HBs experienced secondary vaccine response failure earlier.</p
Booster doses administered to short/long responders and duration of anti-HBs positivity.
<p>Booster doses administered to short/long responders and duration of anti-HBs positivity.</p
Doses of primary hepatitis B vaccine and rate of anti-HBs positivity.
<p>Doses of primary hepatitis B vaccine and rate of anti-HBs positivity.</p