(Non)formation of Methanol by Direct Hydrogenation of Formate on Copper Catalysts

We have attempted to hydrogenate adsorbed formate species on copper catalysts to probe the importance of this postulated mechanistic step in methanol synthesis. Surface formate coverages up to 0,25 were produced at temperatures between 413 and 453 K on supported (Cu/SiO(2)) copper and unsupported copper catalysts. The adlayers were produced; by various methods including (1) steady-state catalytic conditions in CO(2)-H(2) (3:1, 6 bar) atmospheres ad (2) exposure of the catalysts to formic acid. As reported in previous work, the catalytic surface at steady state contains bidentate formate species with coverages up to saturation levels of similar to 0.25 at the law temperatures of this study. The reactivity of these formate adlayers was investigated :it relevant reaction temperatures in atmospheres containing up to 6 bar H(2) partial pressure by simultaneous mass spectrometry (MS) and infrared (IR) spectroscopy measurements. The yield of methanol during the attempted hydrogenation ("titration") of these adlayers was insignificant (<0.2 mol % of the formate adlayer), even in dry hydrogen partial pressures up to 6 bar. Hydrogen titration of formate species produced from formic acid also failed to produce significant quantities of methanol, and attempted titration in consisting of CO-hydrogen mixtures or dry CO(2) was also unproductive. The formate decomposition kinetics, measured by IR, was also unaffected by these changes in the gas composition. Similar experiments on unsupported copper also failed to show any methanol. From these results, we conclude that methanol synthesis on copper cannot result from the direct hydrogenation of (bidentate) formate species in simple steps involving adsorbed H species alone. Furthermore, experiments performed on both supported (Cu/SiO(2)) and unsupported copper catalysts gave similar results, implying that the methanol synthesis reaction mechanism involves only metal surface chemistry. Pre-exposure of the bidentate formate adlayer to oxidation by O(2) or N(2)O produces a change to a monodentate configuration. Attempted titration of this monodentate formate/O coadsorbed layer in dry hydrogen produces significant quantities of methanol, although decomposition of formate to carbon dioxide and hydrogen remains the dominant reaction pathway. Simultaneous production of, water is also observed during this titration as the copper surface is rereduced. These results indicate that coadsorbates related to surface oxygen or water-derived species may be critical to methanol production on copper, perhaps assisting in the hydrogenation of adsorbed formate to adsorbed methoxyl.close1

Representation, Objectivity and the Ethics of Images

This volume features more than 25 papers that were presented at the 2014 Conference of the International Association for the Study of Controversies, IASC, held at the University of Salento, Lecce, Italy. It looks at conflict and conflict resolution from diverse perspectives, including philosophy, psychology, law, and history. Coverage explores the paradox of conflict and examines how discord, whether large or small, international or internal, can be both a source of chaos as well as a foundation for unity, a limitation of potential as well as an entryway to a greater depth of living. Inside, readers will discover thought-provoking answers to such questions as: What are the conditions to ensure that a conflict can be converted into cooperation? If the conflict between interests can be solved by a compromise, what happens when a conflict involves non-negotiable values​​? In the management of a conflict, what role is played by argumentation? What are the latest perspectives in conflict management? How does the theory of controversies allows us to recognize and resolve conflicts? By the end of the book, readers will have a better understanding of how conflict can be transcended and how it's possible to redefine the conflicting situation so that what seemed incompatible and locked may, in fact, open a new perspective