Highly selective CO₂ photoreduction to CO on MOF-derived TiO₂

Metal–Organic Framework (MOF)-derived TiO2, synthesised through the calcination of MIL-125-NH2, is investigated for its potential as a CO2 photoreduction catalyst. The effect of the reaction parameters: irradiance, temperature and partial pressure of water was investigated. Using a two-level design of experiments, we were able to evaluate the influence of each parameter and their potential interactions on the reaction products, specifically the production of CO and CH4. It was found that, for the explored range, the only statistically significant parameter is temperature, with an increase in temperature being correlated to enhanced production of both CO and CH4. Over the range of experimental settings explored, the MOF-derived TiO2 displays high selectivity towards CO (98%), with only a small amount of CH4 (2%) being produced. This is notable when compared to other state-of-the-art TiO2 based CO2 photoreduction catalysts, which often showcase lower selectivity. The MOF-derived TiO2 was found to have a peak production rate of 8.9 × 10−4 μmol cm−2 h−1 (2.6 μmol g−1 h−1) and 2.6 × 10−5 μmol cm−2 h−1 (0.10 μmol g−1 h−1) for CO and CH4, respectively. A comparison is made to commercial TiO2, P25 (Degussa), which was shown to have a similar activity towards CO production, 3.4 × 10−3 μmol cm−2 h−1 (5.9 μmol g−1 h−1), but a lower selectivity preference for CO (3 : 1 CH4 : CO) than the MOF-derived TiO2 material developed here. This paper showcases the potential for MIL-125-NH2 derived TiO2 to be further developed as a highly selective CO2 photoreduction catalyst for CO production

Efficient low-loaded ternary Pd-In2O3-Al2O3 catalysts for methanol production

Pd-In2O3 catalysts are among the most promising alternatives to Cu-ZnO-Al2O3 for synthesis of CH3OH from CO2. However, the intrinsic activity and stability of In2O3 per unit mass should be increased to reduce the content of this scarcely available element and to enhance the catalyst lifetime. Herein, we propose and demonstrate a strategy for obtaining highly dispersed Pd and In2O3 nanoparticles onto an Al2O3 matrix by a one-step coprecipitation followed by calcination and activation. The activity of this catalyst is comparable with that of a Pd-In2O3 catalyst (0.52 vs 0.55 gMeOH h−1 gcat-1 at 300 \ub0C, 30 bar, 40,800 mL h−1 gcat-1) but the In2O3 loading decreases from 98 to 12 wt% while improving the long-term stability by threefold at 30 bar. In the new Pd-In2O3-Al2O3 system, the intrinsic activity of In2O3 is highly increased both in terms of STY normalized to In specific surface area and In2O3 mass (4.32 vs 0.56 g gMeOH h−1 gIn2O3-1 of a Pd- In2O3 catalyst operating at 300 \ub0C, 30 bar, 40,800 mL h−1 gcat-1).The combination of ex situ and in situ catalyst characterizations during reduction provides insights into the interaction between Pd and In and with the support. The enhanced activity is likely related to the close proximity of Pd and In2O3, wherein the H2 splitting activity of Pd promotes, in combination with CO2 activation over highly dispersed In2O3 particles, facile formation of CH3OH

Elucidating the significance of copper and nitrate speciation in Cu-SSZ-13 for N2O formation during NH3-SCR

Unwanted N2O formation is a problem that has been noted in selective catalytic reduction (SCR) where copper zeolite catalysts are utilized. With its immense global warming potential and long-term stability, elevated atmospheric N2O has already been identified as a future challenge in the war on climate change. This paper explores the phenomenon of N2O formation during NH3-SCR over Cu-SSZ-13 catalysts, which are currently commercialized in automotive emissions control systems, and proposes a link between N2O production and the local copper environment found within the zeolite. To achieve this, a comparison is made between two Cu-SSZ-13 samples with different copper co-ordinations produced via different synthesis methods. A combination of synchrotron X-ray absorption near-edge spectroscopy, UV–vis, Raman, and density functional theory (DFT) is used to characterize the nature of copper species present within each sample. Synchrotron IR microspectroscopy is then used to compare their behavior during SCR under operando conditions and monitor the evolution of nitrate intermediates, which, along with further DFT, informs a mechanistic model for nitrate decomposition pathways. Increased N2O production is seen in the Cu-SSZ-13 sample postulated to contain a linear Cu species, providing an important correlation between the catalytic behavior of Cu-zeolites and the nature of their metal ion loading and speciation

Kinetic investigation of the hydrolytic hydrogenation of oligosaccharides to sorbitol

The rare characteristics of sorbitol as a promising intermediate in biomass to biofuel conversion have attracted much research. Nevertheless, adequate understanding of the mechanism and kinetics of its reactions is still missing, mostly because of the complex molecular structure of the polysaccharides that are involved. This dissertation is the tale of our research on the kinetics and mechanism of sorbitol production through hydrolytic hydrogenation of oligosaccharides. Preceding research on this topic is almost entirely based on the controversial hypothesis that conversion of polysaccharides to sorbitol passes through a consecutive hydrolysis to monosaccharides followed by hydrogenation to sorbitol. Our research, on the other hand, reveals two competing reaction pathways, namely hydrolysis of oligosaccharides, and its hydrogenation to reduced form. More interestingly, at lower reaction temperatures the hydrogenation pathway becomes considerably dominant which is contrary to the widely accepted premise. To overcome the molecular complexity of polysaccharides, we settled for model-molecules such as disaccharide and trisaccharide which have simple structure and sufficiently resemble the polysaccharides. Most of our effort has been directed towards selective hydrolysis-hydrogenation of these model molecules over a catalytic system composed of molecular acids and supported metal catalysts. Kinetic study of disaccharide showed that at lower reaction temperatures, the hydrogenation pathway is dominant whereas at higher reaction temperatures, direct hydrolysis of disaccharide becomes favorable. Analysis of kinetic data confirmed the hydrolysis reaction as the rate determining step. Kinetic investigation of trisaccharide also indicated that the hydrogenation proceeds faster than hydrolysis. At the same time, a facilitated hydrolysis of reduced trisaccharide compared with non-reduced counterpart was observed. The study was extended to include oligosaccharides with longer chains, up to heptasaccharides, using the same underlying kinetic model. Despite growing complexity of the reaction network, the same kinetic selectivities i.e. the hydrogenation over hydrolysis as well as facile hydrolysis of reduced compounds were confirmed. Overall, a direct hydrogenation of oligosaccharides to reduced forms followed by hydrolysis appears as a superior sorbitol production pathway

Knowledge, Attitude and Performance of Shiraz General Dentists about Infection Control Principles during Preparing Intraoral Radiographies

Background & Objective: Infection control in dental centers is affected by the persons’ attitude and knowledge about mechanisms of infection transmission. This study was designed to evaluate the knowledge and the attitude of Shiraz dentists about infection control during intraoral radiographies preparation. Materials & Methods: In this cross-sectional, and analytical research, the attitude and the knowledge of 45 male and 25 female, randomly selected dentists, were obtained through completion of a researcher- planed questioner which its validity and reliability had been confirmed. Data were analyzed using Cronbach`s alpha, one-way ANOVA, student’s t-test, and Pearson’s correlation coefficient in SPSS (V.21). Results: The average of the dentists’ age was 40.59±10.72 and their average occupational experience was 13.49±9.75 years. The mean score obtained for knowledge about infection control during intraoral radiographic procedures was less than fifty percent of total obtainable score, and was assessed as weak knowledge. There was no significant difference in the level of knowledge between studied male and female dentists (P>0.05). In addition, no significant relationship was detected between level, age/experience, and the university of education (P>0.05). The attitude of the dentists about infection control during intraoral radiography preparation assessed as moderate to good level. Conclusions: The results showed that the main reason for the present problems is insufficient knowledge of the dentists in related subjects. Therefore, the solution, which is recommended among dentists, is to raise their awareness and to change their attitudes and culture in order to improve their performance

Mechanistic Aspects of the Electrocatalytic Oxygen Evolution Reaction over Ni−Co Oxides

The electrocatalytic oxygen evolution reaction (OER) presents the key transformation in electrochemical water‐splitting majorly determining energy efficiency and economics of hydrogen generation. In this study, the kinetics of the OER over Ni‐Co oxide structured by KIT‐6 templating and non‐structured Ni‐Co oxide catalysts in alkaline solution have been investigated aiming for insight with regard to the respective kinetically relevant surface reactions. Steady‐state Tafel plot analysis and electrochemical impedance spectroscopy (EIS) were used to determine kinetic parameters, Tafel slopes and the order of reaction. A dual Tafel slope behavior was observed for both catalysts. Tafel slopes of ca. 40 and 120 mV dec‐1 and 90 and 180 mV dec‐1 at low and high overpotentials appear for structured and non‐structured Ni‐Co oxide, respectively. A reaction order of unity was observed for structured Ni‐Co oxide, while non‐structured Ni‐Co oxide possessed a fractional reaction order in the high overpotential region. The kinetics of OER over structured Ni‐Co oxide were governed by Langmuir adsorption with the rate‐limiting step after primary adsorption of surface intermediates. In contrast, non‐structured Ni Co oxide obeyed the Temkin adsorption isotherm condition with the primary adsorption step being rate‐limiting