Role of Surface Species Interactions in Identifying the Reaction Mechanism of Methanol Synthesis from CO₂ Hydrogenation over Intermetallic PdIn(310) Steps

Considerable attention has been paid to the development of new catalysts for methanol synthesis from CO2 hydrogenation for a long period of time. The PdIn intermetallic catalyst was found recently to exhibit good stability and activity for methanol formation. We thus performed a theoretical study to understand the reaction mechanism of methanol synthesis on stepped PdIn(310), combining density functional theory (DFT) calculations and microkinetic analysis. On the basis of energetics obtained on clean PdIn(310), we found that the preferred reaction pathway for CH3OH generation proceeds through the COOH intermediate and further CO hydrogenation. However, microkinetic results suggested that the coverage of formate and carbon monoxide at the steady state is nearly one monolayer at the corresponding preferred adsorption site, that is, the In site for HCOO and the Pd site for CO, within the whole temperature range studied. Therefore, further studies were carried out to reveal the influence of coverage of preadsorbed formate and carbon monoxide on adsorption energies. It turned out that the differential adsorption energy of formate at the In site is comparable to that at the Pd site when the surface is covered by two formate at the In step-bridge site, indicating that it is possible for an additional formate to adsorb at either the Pd or In site under such condition. On this basis, we found with further DFT calculations and microkinetic analysis that the preferred reaction mechanism of methanol formation would change to the one including the HCOOH intermediate and the reaction prefers to happen at the Pd site, with two formate preadsorbing at the In step-bridge site at the same time. It was found that such changes can be attributed to the reduced barriers of elementary steps in this path introduced by the formate coverage effect. Therefore, it is imperative to carry out a theoretical study for surface reactions by combining DFT calculations and microkinetic analysis and to take the interactions between dominant surface species into account when identifying the mechanism under reaction conditions

One of the 316 parsimonious trees derived from rpb2 sequence data was conducted using heuristic search with TBR branch swapping.

<p>Numbers above and below branches are bootstrap values from MP and Bayesian posterior probability (PP) values, respectively. <i>Bromus inermis</i> was used as an outgroup. Consistency index (CI) = 0.791, retention index (RI) = 0.932.</p

Essential Role of Water in the Autocatalysis Behavior of Methanol Synthesis from CO₂ Hydrogenation on Cu: A Combined DFT and Microkinetic Modeling Study

Water is able to promote many chemical reactions in an autocatalysis manner, and the essential role that water plays in the system is still worth discussing. In the process of methanol synthesis from CO2 hydrogenation on Cu, whether the promoting species is molecular water or water derived O/OH is controversial. To systematically understand the influence of the presence of O/OH on the reaction kinetics of CO2 hydrogenation to methanol, we here carry out density functional theory calculations to obtain the energetics over O/OH preadsorbed Cu(211) and further use them for microkinetic modeling in order to calculate the formation rate of methanol. The calculation results show that the free energy barriers of CO2 activation by molecular water through both HCOO and COOH routes are higher than those by the hydrogen atom on clean and OH or O preadsorbed Cu(211). The subsequent microkinetic modeling indicates that the formation rate of methanol over Cu(211) is improved in the presence of O/OH. Detailed analyses on the coverage and degree of rate control of surface species reveal that the presence of O/OH on the catalyst surface will destabilize the spectating formate and lower the energies of rate-controlling transition states. The formate coverage effect is further included in the microkinetic modeling, and we find that the reaction rate is further increased at lower temperatures. Our current work provides evidence that the surface adsorbed O and OH are able to promote the formation of methanol from CO2 hydrogenation and, more importantly, highlights the fact that the activity of methanol formation is sensitive to the surface adsorbates

Multiple copies of the pepc sequences recovered from H genome of <i>Elymus trachycaulus</i> with relative large insertion/deletion, which might be caused by gene instabilities.

<p>Multiple copies of the pepc sequences recovered from H genome of <i>Elymus trachycaulus</i> with relative large insertion/deletion, which might be caused by gene instabilities.</p

One of the 570 parsimonious trees derived from <i>pepc</i> sequence data was conducted using heuristic search with TBR branch swapping.

<p>Numbers above and below branches are bootstrap values from MP and Bayesian posterior probability (PP) values, respectively. <i>Bromus tectorum</i> was used as an outgroup. Consistency index (CI) = 0.735, retention index (RI) = 0.906.</p

Taxa from <i>Bromus</i>, <i>Aegilops</i>, <i>Eremopyrum</i>, <i>Heteranthelium</i>, <i>Psathyrostachys</i>, <i>Secale</i>, <i>Taeniatherum</i>, <i>Agropyron</i>, <i>Australopyrum</i>, <i>Dasypyrum</i>, <i>Thinopyrum</i>, <i>Triticum</i>, <i>Pseudoroegneria</i>, <i>Hordeum</i> and <i>Elymus</i> used in this study, their origin, accession number and GenBank sequence number.

<p>NA: information not available; +: sequence present,-: sequence absent</p><p>Taxa from <i>Bromus</i>, <i>Aegilops</i>, <i>Eremopyrum</i>, <i>Heteranthelium</i>, <i>Psathyrostachys</i>, <i>Secale</i>, <i>Taeniatherum</i>, <i>Agropyron</i>, <i>Australopyrum</i>, <i>Dasypyrum</i>, <i>Thinopyrum</i>, <i>Triticum</i>, <i>Pseudoroegneria</i>, <i>Hordeum</i> and <i>Elymus</i> used in this study, their origin, accession number and GenBank sequence number.</p

One of the 134 parsimonious trees derived from <i>TrnL/F</i> sequence data was conducted using heuristic search with TBR branch swapping.

<p>Numbers above branches are MP bootstrap values and Bayesian posterior probability (PP) values, respectively. <i>Bromus tectorum</i> was used as an outgroup. Consistency index (CI) = 0.903, retention index (RI) = 0.941.</p

Improved Whole-Cell Biocatalyst for the Synthesis of Vitamin E Precursor 2,3,5-Trimethylhydroquinone

2,3,5-Trimethylhydroquinone (2,3,5-TMHQ) is the key precursor in the synthesis of vitamin E. It is still a major challenge to produce 2,3,5-TMHQ under mild reaction conditions by chemical methods. The monooxygenase system MpdAB can specifically catalyze the conversion of 2,3,6-trimethylphenol (2,3,6-TMP) to 2,3,5-TMHQ. However, the weak catalytic capacity of wild-type MpdA and the cytotoxicity of the substrate limited the production efficiency of 2,3,5-TMHQ. Here, homologous modeling and saturation mutation were performed to increase the catalytic activity of MpdA. Two variants, L128A and L128K, with higher activity toward 2,3,6-TMP (1.86–1.87-fold) were obtained. On the other hand, an evolved strain B5-4M-evolved with enhanced resistance to 2,3,6-TMP (8.15-fold higher for 1000 μM 2,3,6-TMP) was obtained through adaptive laboratory evolution. Subsequently, a 5.29-fold (or 4.87-fold) improvement in 2,3,5-TMHQ production was achieved by a strain B5-4M-evolved harboring L128K (or L128A) and MpdB, in comparison with that of the wild type (strain B5-4M expressing MpdAB). This study provides better genetic resources for producing 2,3,5-TMHQ and proves that the synthesis efficiency of 2,3,5-TMHQ can be improved through enzyme modification and adaptive laboratory evolution