Dehydrogenation of 3-carene in the vapour phase. II. Performance studies of chromia and chromia-alumina catalysts

1980 ◽  
Vol 33 (6) ◽  
pp. 1313 ◽  
Author(s):  
V Krishnasamy
Keyword(s):  
Water Vapour ◽  
Performance Studies ◽  
Active Sites ◽  
Vapour Phase ◽  
Progressive Increase ◽  
Oxidation States ◽  
Side Reactions ◽  
Potassium Ions ◽  
Alumina Catalyst ◽  
Alumina Catalysts

The influence of contact time on the dehydrogenation of 3-carene over reduced chromia and chromia-alumina catalysts has been investigated at 450 and 400°C respectively. For the dehydrogenation, reduced chromia- alumina catalyst is more active than reduced chromia alone. It has been found that the dehydrogenating ability of reduced chromia is superior to that of oxidized chromia. The effect of water vapour on reduced chromia showed an initial suppression of its reactivity, but at intermediate values increased its activity. Progressive increase of water vapour was seen to modify the active sites of reduced chromia, an effect similar to that of the oxidized sample. ��� The dehydrogenation of 3-carene, over chromia, follows second-order kinetics. The energy of activation is found to be greater for oxidized than for reduced chromia. Impregnation of chromia with potassium decreases the activation energy of reduced chromia and enhances its dehydrogenation ability by suppressing the side reactions. ��� The observed experimental data are explained in terms of the acidity of the catalysts, oxidation states of chromium ions and the promoting influence of potassium ions.

Vapour phase catalytic transformations of terpene hydrocarbons in the C10H16 series. III. Dehydrogenation of Δ3-carene over modified chromia and chromia–alumina catalysts

1976 ◽  
Vol 54 (21) ◽  
pp. 3458-3463 ◽  
Author(s):  
V. Krishnasamy ◽  
L. M. Yeddanapalli
Keyword(s):  
Hydrofluoric Acid ◽  
Vapour Phase ◽  
Potassium Ions ◽  
Total Conversion ◽  
Fluoride Ions ◽  
Catalytic Transformations ◽  
Alumina Catalysts

The vapour phase dehydrogenation of 3-carene has been studied over chromia, chromia–alumina, chromia doped with potassium, and chromia–alumina doped with potassium and fluoride ions. Addition of potassium to chromia and chromia–alumina up to 1% by weight does not significantly affect the overall conversion of 3-carene whereas it increases its dehydrogenation to p- and m-cymenes. Potassium ions above 1% lower both the total conversion and dehydrogenation of 3-carene to cymenes. The ratio of p- to m-cymene over chromia–alumina is enhanced by added potassium ions up to 2%, but over chromia it remains unaffected. Addition of potassium to chromia decreases the formation of menthanes and menthadienes but its addition to chromia–alumina reduces the formation of menthanes and increases that of menthadienes. Impregnation of chromia–alumina with hydrofluoric acid suppresses the formation of menthadienes and increases that of menthanes. All these are explained in terms of the effect of added potassium and fluoride ions on the acidity of the catalysts.

Synthetic models for active sites of reduced blue copper proteins: minimal geometric change between two oxidation states for fast self-exchange rate constants

2004 ◽  
Vol 7 (11) ◽  
pp. 1188-1190 ◽  
Author(s):  
Kiyoshi Fujisawa ◽  
Koyu Fujita ◽  
Tatsuya Takahashi ◽  
Nobumasa Kitajima ◽  
Yoshihiko Moro-oka ◽  
...  
Keyword(s):  
Exchange Rate ◽  
Rate Constants ◽  
Active Sites ◽  
Oxidation States ◽  
Copper Proteins ◽  
Blue Copper Proteins ◽  
Blue Copper ◽  
Synthetic Models

scholarly journals Evaluation of a Catalyst Durability in Absence and Presence of Toluene Impurity: Case of the Material Co2Ni2Mg2Al2 Mixed Oxide Prepared by Hydrotalcite Route in Methane Dry Reforming to Produce Energy

Materials ◽  
2019 ◽  
Vol 12 (9) ◽  
pp. 1362
Author(s):  
Carole Tanios ◽  
Cédric Gennequin ◽  
Madona Labaki ◽  
Haingomalala Lucette Tidahy ◽  
Antoine Aboukaïs ◽  
...  
Keyword(s):  
Catalytic Activity ◽  
Mixed Oxide ◽  
Active Sites ◽  
Dry Reforming ◽  
Dry Reforming Of Methane ◽  
Side Reactions ◽  
Commercial Catalyst ◽  
Catalytic Sites ◽  
Catalyst Durability ◽  
Catalytic Performances

Ni, Co, Mg, and Al mixed-oxide solids, synthesized via the hydrotalcite route, were investigated in previous works toward the dry reforming of methane for hydrogen production. The oxide Co2Ni2Mg2Al2 calcined at 800 °C, Co2Ni2Mg2Al2800, showed the highest catalytic activity in the studied series, which was ascribable to an interaction between Ni and Co, which is optimal for this Co/Ni ratio. In the present study, Co2Ni2Mg2Al2800 was compared to a commercial catalyst widely used in the industry, Ni(50%)/Al2O3, and showed better activity despite its lower number of active sites, as well as lower amounts of carbon on its surface, i.e. less deactivation. In addition to this, Co2Ni2Mg2Al2800 showed stability for 20 h under stream during the dry reforming of methane. This good durability is attributed to a periodic cycle of carbon deposition and removal as well as to the strong interaction between Ni and Co, preventing the deactivation of the catalyst. The evaluation of the catalytic performances in the presence of toluene, which is an impurity that exists in biogas, is also a part of this work. In the presence of toluene, the catalytic activity of Co2Ni2Mg2Al2800 decreases, and higher carbon formation on the catalyst surface is detected. Toluene adsorption on catalytic sites, side reactions performed by toluene, and the competition between toluene and methane in the reaction with carbon dioxide are the main reasons for such results.

Catalytic routes to fuels from C1 and oxygenate molecules

2017 ◽  
Vol 197 ◽  
pp. 9-39 ◽  
Author(s):  
Shuai Wang ◽  
Iker Agirrezabal-Telleria ◽  
Aditya Bhan ◽  
Dante Simonetti ◽  
Kazuhiro Takanabe ◽  
...  
Keyword(s):  
Transition State ◽  
Active Sites ◽  
Aldol Condensation ◽  
Bond Formation ◽  
Transition States ◽  
Solid Acids ◽  
State Theory ◽  
Side Reactions ◽  
Oh Radicals ◽  
Acid Base

This account illustrates concepts in chemical kinetics underpinned by the formalism of transition state theory using catalytic processes that enable the synthesis of molecules suitable as fuels from C1 and oxygenate reactants. Such feedstocks provide an essential bridge towards a carbon-free energy future, but their volatility and low energy density require the formation of new C–C bonds and the removal of oxygen. These transformations are described here through recent advances in our understanding of the mechanisms and site requirements in catalysis by surfaces, with emphasis on enabling concepts that tackle ubiquitous reactivity and selectivity challenges. The hurdles in forming the first C–C bond from C1 molecules are illustrated by the oxidative coupling of methane, in which surface O-atoms form OH radicals from O2 and H2O molecules. These gaseous OH species act as strong H-abstractors and activate C–H bonds with earlier transition states than oxide surfaces, thus rendering activation rates less sensitive to the weaker C–H bonds in larger alkane products than in CH4 reactants. Anhydrous carbonylation of dimethyl ether forms a single C–C bond on protons residing within inorganic voids that preferentially stabilize the kinetically-relevant transition state through van der Waals interactions that compensate for the weak CO nucleophile. Similar solvation effects, but by intrapore liquids instead of inorganic hosts, also become evident as alkenes condense within MCM-41 channels containing isolated Ni2+ active sites during dimerization reactions. Intrapore liquids preferentially stabilize transition states for C–C bond formation and product desorption, leading to unprecedented reactivity and site stability at sub-ambient temperatures and to 1-alkene dimer selectivities previously achieved only on organometallic systems with co-catalysts or activators. C1 homologation selectively forms C4 and C7 chains with a specific backbone (isobutane, triptane) on solid acids, because of methylative growth and hydride transfer rates that reflect the stability of their carbenium ion transition states and are unperturbed by side reactions at low temperatures. Aldol condensation of carbonyl compounds and ketonization of carboxylic acids form new C–C bonds concurrently with O-removal. These reactions involve analogous elementary steps and occur on acid–base site pairs on TiO2 and ZrO2 catalysts. Condensations are limited by α-H abstraction to form enolates via concerted interactions with predominantly unoccupied acid–base pairs. Ketonization is mediated instead by C–C bond formation between hydroxy-enolates and monodentate carboxylates on site pairs nearly saturated by carboxylates. Both reactions are rendered practical through bifunctional strategies, in which H2 and a Cu catalyst function scavenge unreactive intermediates, prevent sequential reactions and concomitant deactivation, and remove thermodynamic bottlenecks. Alkanal–alkene Prins condensations on solid acids occur concurrently with alkene dimerization and form molecules with new C–C bonds as skeletal isomers unattainable by other routes. Their respective transition states are of similar size, leading to selectivities that cannot sense the presence of a confining host. Prins condensation reactions benefit from weaker acid sites because their transition states are less charged than those for oligomerization and consequently less sensitive to conjugate anions that become less stable as acids weaken.

Silver-alumina catalysts for selective reduction of NO by higher hydrocarbons: structure of active sites and reaction mechanism

2001 ◽  
Vol 30 (1-2) ◽  
pp. 151-162 ◽  
Author(s):  
Ken-ichi Shimizu ◽  
Junji Shibata ◽  
Hisao Yoshida ◽  
Atsushi Satsuma ◽  
Tadashi Hattori
Keyword(s):  
Reaction Mechanism ◽  
Active Sites ◽  
Selective Reduction ◽  
Reduction Of No ◽  
Higher Hydrocarbons ◽  
Alumina Catalysts

Delafossite Nanoparticle as New Functional Materials: Advances in Energy, Nanomedicine and Environmental Applications

2015 ◽  
Vol 832 ◽  
pp. 28-53 ◽  
Author(s):  
Hani Nasser Abdelhamid
Keyword(s):  
Active Sites ◽  
Energy Gap ◽  
Functional Materials ◽  
Oxidation States ◽  
Structure Modification ◽  
Small Energy ◽  
Bioactive Materials ◽  
Promising Application ◽  
Electrochemical Devices ◽  
Future Status

Recently, numerous delafossite oxides in nanoscale have been reported for diverse applications. The present review summarized the recent overall views of delafossite nanoparticles in diverse applications such as energy, catalysis, photocatalysis, nanomedicine, sensors, electrochemical devices and environmental concerns. Delafossite nanoparticles possess unique features such as different and wide chemical composition, large surface area, small energy gap, ability for further functionalization, possess dual-active sites with different oxidation states (A+and M3+), and eager for doping with various species with feasibility to undergo structure modification. Thus, they provided promising application such as solar cell, photocatalysis, hydrogen production, bioactive materials, separation purposes and others. Pros, cons, current and future status were also reviewed.

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