Selecting Double Bond Positions with a Single Cation- Responsive Iridium Olefin Isomerization Catalyst

<div><div><div><p>The catalytic transposition of double bonds holds promise as an ideal route to alkenes with value as fragrances, commodity chemicals, and pharmaceuticals; yet, selective access to specific isomers is a challenge, requiring independent development of different catalysts for different products. In this work, a single cation-responsive iridium catalyst is developed for the selective production of either of two different internal alkene isomers. In the absence of salts, a single positional isomerization of 1-butene derivatives furnishes 2-alkenes with exceptional regioselectivity and stereoselectivity. The same catalyst, in the presence of Na+, mediates two positional isomerizations to produce 3-alkenes. The synthesis of new iridium pincer-crown ether catalysts based on an aza-18-crown-6 ether proved instrumental in achieving cation-controlled selectivity. Experimental and computational studies guided the development of a mechanistic model that explains the observed selectivity for various functionalized 1-butenes, providing insight into strategies for catalyst development based on non-covalent modifications.</p></div></div></div>

Selecting Double Bond Positions with a Single Cation- Responsive Iridium Olefin Isomerization Catalyst

<div><div><div><p>The catalytic transposition of double bonds holds promise as an ideal route to alkenes with value as fragrances, commodity chemicals, and pharmaceuticals; yet, selective access to specific isomers is a challenge, requiring independent development of different catalysts for different products. In this work, a single cation-responsive iridium catalyst is developed for the selective production of either of two different internal alkene isomers. In the absence of salts, a single positional isomerization of 1-butene derivatives furnishes 2-alkenes with exceptional regioselectivity and stereoselectivity. The same catalyst, in the presence of Na+, mediates two positional isomerizations to produce 3-alkenes. The synthesis of new iridium pincer-crown ether catalysts based on an aza-18-crown-6 ether proved instrumental in achieving cation-controlled selectivity. Experimental and computational studies guided the development of a mechanistic model that explains the observed selectivity for various functionalized 1-butenes, providing insight into strategies for catalyst development based on non-covalent modifications.</p></div></div></div>

Effect of the Cr2O3 Promoter on Pt/WO3-ZrO2 Catalysts for n-Heptane Isomerization

Isomerate, the product of a light naphtha Isomerization unit, is a clean, high-octane gasoline blending component, which is free of sulfur content, aromatics, and olefins. However, the isomerization of the long-chain alkanes, such as n-heptane, is pretty difficult. As a result, this process has not been commercialized yet. In recent years, much attention has been paid to Pt/WO3/ZrO2 as an n-heptane isomerization catalyst due to its good thermal stability, strong acidity, simplicity of preparation, reusability and good isomerization activity. In this work, the Pt/WO3/ZrO2 catalyst was modified by various loading of metal Cr to improve the catalytic performance. The effects of WO3 content, Cr metal loading and calcination temperature on the catalyst characters and catalytic activity were studied. It is shown that Cr-Pt/WO3/ZrO2 with the loading of 18 wt% WO3 and 1.0–1.4 wt% Cr, prepared at the calcination temperature of 800 °C, has the highest activity. It was found that the octane number increases by 28 units through the isomerization of light naphtha feedstocks. In addition, the study on the stability of Cr-Pt/WO3/ZrO2 indicates that the catalyst is not deactivated after 500 h of the n-heptane isomerization reaction.

Facile Fabrication of Hollow Li3PO4 Catalyst via Ostwald Ripening

Hollow inorganic nanostructures are important due to their applications in energy storage and conversion, catalysis, gas sensing, and biomedicine. Li3PO4 is used as an isomerization catalyst for propylene oxide to selectively give allyl alcohol. We used a facile template-free method to synthesize hollow Li3PO4 nanoparticles with size range of 500[Formula: see text]nm to 1500[Formula: see text]nm. The effect of concentration, agitation, ripening temperature and the ratio of starting reagents on the hollowing process is investigated. The most important factor to influence the hollowness was found to be the ratio of lithium ion to phosphate ion; as the ratio increases, the hollowness of the particles increases. When this ratio reached 3, the hollow nanostructures become dominant. As an isomerization catalyst for propylene oxide, 4-Li3PO4 exhibited the highest conversion and best selectivity of allyl alcohol. The hydroxide ion of the precursor is adsorbed on the surface of the Li3PO4 particles which results in different surface basicity.

Deactivation of Chlorinated Pt/Al2O3 Isomerization Catalyst Using Water Containing Feed

Light naphtha isomerization is a significant process in a crude oil refinery which is responsible for upgrading low-octane light naphtha to the high-octane and low-aromatic content gasoline. In this work, deactivation of an industrial chlorinated Pt/Al2O3 isomerization catalyst was studied in a laboratory scale plant. Experiments were carried out under temperatures in the range of 120–180 °C, liquid hourly space velocities (LHSV) of 0.7–2 h−1 and hydrogen to hydrocarbon molar ratios (H2/Oil) of 0.7–1.5. Moreover, the total water content of the combined feed, i. e. n-hexane and hydrogen, was 70 ppmwt. During 75 h time on stream (TOS), 42 data sets were collected and applied for training, testing and validating a hybrid-artificial neural network model (hybrid-ANN or HANN) to estimate the activity of the catalyst. Results showed that the activity decreased to 0.56 at the end of the operation mostly due to water poisoning. Furthermore, using the estimated activity, HANN could simulate the conversion and selectivity of the isomerization process with the absolute average deviations (AAD%) of 0.97 % and 0.0766 % and the mean squared errors (MSE) of 0.311 and 0.0156, respectively.

Alkene-assisted cis-to-trans isomerization of non-conjugated polyunsaturated alkenes

Complex [Cp*Ru(NCMe)3][PF6], 1a, has been identified as a cis-to-trans isomerization catalyst of various non-conjugated cis-polyalkenes under exceptional kinetic control as no alkene conjugation was observed.