Hydrotalcite-type anionic clays: Preparation, properties and applications.

and Fuels Changzhi Li,† Xiaochen Zhao,† Aiqin Wang,† George W. Huber,†,‡ and Tao Zhang*,† †State Key Laborotary of Catalysis, iChEM (Collaborative Innovation Center of Chemistry for Energy Materials), Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China ‡Department of Chemical and Biological Engineering, University of WisconsinMadison, Madison, Wisconsin 53706, United States

Catalytic Transformation of Lignin for the Production of Chemicals and Fuels

As the oil reserves are depleting the need of an alternative fuel source is becoming increasingly apparent. One prospective method for producing fuels in the future is conversion of biomass into bio-oil and then upgrading the bio-oil over a catalyst, this method is the focus of this review article. Bio-oil production can be facilitated through flash pyrolysis, which has been identified as one of the most feasible routes. The bio-oil has a high oxygen content and therefore low stability over time and a low heating value. Upgrading is desirable to remove the oxygen and in this way make it resemble crude oil. Two general routes for bio-oil upgrading have been considered: hydrodeoxygenation (HDO) and zeolite cracking. HDO is a high pressure operation where hydrogen is used to exclude oxygen from the bio-oil, giving a high grade oil product equivalent to crude oil. Catalysts for the reaction are traditional hydrodesulphurization (HDS) catalysts, such as Co–MoS2/Al2O3, or metal catalysts, as for example Pd/C. However, catalyst lifetimes of much more than 200 h have not been achieved with any current catalyst due to carbon deposition. Zeolite cracking is an alternative path, where zeolites, e.g. HZSM-5, are used as catalysts for the deoxygenation reaction. In these systems hydrogen is not a requirement, so operation is performed at atmospheric pressure. However, extensive carbon deposition results in very short catalyst lifetimes. Furthermore a general restriction in the hydrogen content of the bio-oil results in a low H/C ratio of the oil product as no additional hydrogen is supplied. Overall, oil from zeolite cracking is of a low grade, with heating values approximately 25% lower than that of crude oil. Of the two mentioned routes, HDO appears to have the best potential, as zeolite cracking cannot produce fuels of acceptable grade for the current infrastructure. HDO is evaluated as being a path to fuels in a grade and at a price equivalent to present fossil fuels, but several tasks still have to be addressed within this process. Catalyst development, understanding of the carbon forming mechanisms, understanding of the kinetics, elucidation of sulphur as a source of deactivation, evaluation of the requirement for high pressure, and sustainable sources for hydrogen are all areas which have to be elucidated before commercialisation of the process.

A review of catalytic upgrading of bio-oil to engine fuels

Single- and multilayer MoS(2) films are deposited onto Si/SiO(2) using the mechanical exfoliation technique. The films were then used for the fabrication of field-effect transistors (FETs). These FET devices can be used as gas sensors to detect nitrous oxide (NO). Although the single-layer MoS(2) device shows a rapid response after exposure to NO, the current was found to be unstable. The two-, three-, and four-layer MoS(2) devices show both stable and sensitive responses to NO down to a concentration of 0.8 ppm.

Fabrication of Single‐ and Multilayer MoS2 Film‐Based Field‐Effect Transistors for Sensing NO at Room Temperature

Opportunities and prospects in the chemical recycling of carbon dioxide to fuels

Recent literature on synthesis gas conversion to higher alcohols over Mo-based catalysts is reviewed. Density functional theory calculations show that Mo-CO adsorption is weakened by C, P, or S lig...

A Review of Molybdenum Catalysts for Synthesis Gas Conversion to Alcohols: Catalysts, Mechanisms and Kinetics

A study of the hydrodeoxygenation (HDO) of 4-methylphenol over unsupported, low-surface-area MoS2, MoO2, MoO3, and MoP catalysts is reported. With the exception of MoO3, the catalysts had the same physicochemical properties before and after the 5 h reaction at 623 K and 4.40 MPa H2. The used MoO3 was partially reduced to a mixed oxide containing Mo4O11, MoO2, and Mo. Compared to the unused MoO3, the used MoO3 CO uptake increased by a factor of 100 following the reaction. The partially reduced Mo oxide catalyst had a high conversion for the HDO of 4-methylphenol because of Bronsted acid sites and the formation of anionic vacancies. The catalyst turnover frequency (TOF) based on CO uptake for the HDO of 4-methylphenol decreased in the order MoP > MoS2 > MoO2 > MoO3, while the activation energy increased in the order of MoP < MoS2 < MoO2 < MoO3. The activity trends correspond to the increased electron density of the Mo among the catalysts. Two primary reactions, C−O hydrogenolysis to yield toluene and satura...

Hydrodeoxygenation of 4-Methylphenol over Unsupported MoP, MoS2, and MoOx Catalysts†

Background: Cricoid pressure (CP) is often used during general anesthesia induction to prevent passive regurgitation of gastric contents. The authors used magnetic resonance imaging to determine the anatomic relationship between the esophagus and the cricoid cartilage (“cricoid”) with and without CP. Methods: Magnetic resonance images of the necks of 22 healthy volunteers were reviewed with and without CP. Esophageal and airway dimensions, distance between the midline of the vertebral body and the midline of the esophagus, and distance between the lateral border of the cricoid or vertebral body and the lateral border of the esophagus were measured. Results: The esophagus was displaced laterally relative to the cricoid in 52.6% of necks without CP and 90.5% with CP. CP shifted the esophagus relative to its initial position to the left in 68.4% of subjects and to the right in 21.1% of subjects. Unopposed esophagus was seen in 47.4% of necks without CP and 71.4% with CP. Lateral laryngeal displacement and airway compression were demonstrated in 66.7% and 81.0% of necks, respectively, as a result of CP. Conclusion: In the absence of CP, the esophagus was lateral to the cricoid in more than 50% of the sample. CP further displaced both the esophagus and the larynx laterally. SINCE the description by Sellick 1 in 1961, cricoid pres

Cricoid Pressure Displaces the Esophagus: An Observational Study Using Magnetic Resonance Imaging

Effects of H2O on the activity and deactivation of Pd catalysts used for the oxidation of unburned CH4 present in the exhaust gas of natural-gas vehicles (NGVs) are reviewed. CH4 oxidation in a catalytic converter is limited by low exhaust gas temperatures (500–550 °C) and low concentrations of CH4 (400–1500 ppmv) that must be reacted in the presence of large quantities of H2O (10–15%) and CO2 (15%), under transient exhaust gas flows, temperatures, and compositions. Although Pd catalysts have the highest known activity for CH4 oxidation, water-induced sintering and reaction inhibition by H2O deactivate these catalysts. Recent studies have shown the reversible inhibition by H2O adsorption causes a significant drop in catalyst activity at lower reaction temperatures (below 450 °C), but its effect decreases (water adsorption becomes more reversible) with increasing reaction temperature. Thus above 500 °C H2O inhibition is negligible, while Pd sintering and occlusion by support species become more important. H2O inhibition is postulated to occur by either formation of relatively stable Pd(OH)2 and/or partial blocking by OH groups of the O exchange between the support and Pd active sites thereby suppressing catalytic activity. Evidence from FTIR and isotopic labeling favors the latter route. Pd catalyst design, including incorporation of a second noble metal (Rh or Pt) and supports high O mobility (e.g., CeO2) are known to improve catalyst activity and stability. Kinetic studies of CH4 oxidation at conditions relevant to natural gas vehicles have quantified the thermodynamics and kinetics of competitive H2O adsorption and Pd(OH)2 formation, but none have addressed effects of H2O on O mobility.

Deactivation of Pd Catalysts by Water during Low Temperature Methane Oxidation Relevant to Natural Gas Vehicle Converters

A study of the hydrodeoxygenation (HDO) of 4-methylphenol over unsupported, low-surface-area MoS 2 , MoO 2 , MoO 3 , and MoP catalysts is reported. With the exception of MoO 3 , the catalysts had the same physicochemical properties before and after the 5 h reaction at 623 K and 4.40 MPa H 2 . The used MoO 3 was partially reduced to a mixed oxide containing Mo 4 O 11 , MoO 2 , and Mo. Compared to the unused MoO 3 , the used MoO 3 CO uptake increased by a factor of 100 following the reaction. The partially reduced Mo oxidecatalyst had a high conversion for the HDO of4-methylphenol because of Bronsted acid sites and the formation ofanionic vacancies. The catalyst turnover frequency (TOF) based on CO uptake for the HDO of 4-methylphenol decreased in the order MoP > MoS z > MoO 2 > MoO 3 , while the activation energy increased in the order of MoP < MoS 2 < MoO 2 < MoO 3 . The activity trends correspond to the increased electron density of the Mo among the catalysts. Two primary reactions, C―O hydrogenolysis to yield toluene and saturation of 4-methylphenol followed by rapid dehydration to produce 4-methylcyclohexene, were identified. The catalysts differed in their hydrogenation and isomerization capabilities. The MoP catalyst displayed the highest selectivity toward hydrogenated products, suggesting that the rate-limiting step over MoO 3 , MoO 2 , and MoS 2 was the saturation of 4-methylphenol to produce 4-methylcyclohexanol.

Kevin J. Smith

Papers

A Review of Molybdenum Catalysts for Synthesis Gas Conversion to Alcohols: Catalysts, Mechanisms and Kinetics

Hydrodeoxygenation of 4-Methylphenol over Unsupported MoP, MoS2, and MoOx Catalysts†

Cricoid Pressure Displaces the Esophagus: An Observational Study Using Magnetic Resonance Imaging

Deactivation of Pd Catalysts by Water during Low Temperature Methane Oxidation Relevant to Natural Gas Vehicle Converters

Hydrodeoxygenation of 4-Methylphenol over Unsupported MoP, MoS2, and MoOx Catalysts