Minimizing energy demand and environmental impact for sustainable NH3 and H2O2 production—A perspective on contributions from thermal, electro-, and photo-catalysis

There is an urgent need to provide adequate and sustainable supplies of water and food to satisfy the demand of an increasing population. Catalysis plays important roles in meeting these needs by facilitating the synthesis of hydrogen peroxide that is used in water decontamination and chemicals production, and ammonia that is used as fertilizer. However, these chemicals are currently produced with processes that are either very energy-intensive or environmentally unfriendly. This article offers the perspectives of the challenges and opportunities in the production of these chemicals, focusing on the roles of catalysis in more sustainable, alternative production methods that minimize energy consumption and environmental impact. While not intended to be a comprehensive review, the article provides a critical review of selected literature relevant to its objectives, discusses areas needed for further research, and potential new directions inspired by new developments in related fields. For each chemical, production by thermal, electro-, and photo-excited processes are discussed. Problems that are common to these approaches and their differences are identified and possible solutions suggested

Novel technologies for SO{sub x}/NO{sub x} removal from flue gas

The goal of this project is to develop a cost-effective low temperature deNO{sub x} process. NO{sub x} removal at temperatures between 120C--150C was investigated using the approaches of (1) selective reduction of NO{sub x} by alcohol or acetone (2) adsorption of NO{sub x} with an effective sorbent. The chief problem encountered in low temperature reduction of NO was catalyst deactivation due to coke formation. In this quarter, a possible solution explored was increasing the loading of precious metals (Pd and Ag) on oxide supports, as precious metals are known to be effective in the oxidation of hydrocarbons at low temperatures. However, no improvement was observed. Another solution was the replacement of NO by NO{sub 2} in the feed for the carbon-based catalyst tested, as NO{sub 2} was observed to slow down the deactivation rate over Cu-ZrO{sub 2} catalyst. However, rapid reduction of NO{sub 2} to NO by the carbon support occurred, making this approach impractical. As part of this approach, search for better NO oxidation catalysts continued this quarter. It was found that on different carbon catalysts at 30C and a W/F of 0.01g.min/cc, NO conversion to NO{sub 2} between 82--90% can be achieved. This activity, however, decreased with increasing temperature. SO{sub 2} also poisoned the oxidation activity of the activated carbon. Au dispersed on lanthanum oxide was another catalyst tested and had an NO conversion to NO{sub 2} of 17% at 250C. The catalytic performance of this catalyst could be improved by increasing its surface area. Finally, the adsorption capacity of NO{sub x} of a carbon sample provided by ISGS and an inorganic sorbent were tested. The capacity of the inorganic sorbent was found to be much higher

Addition of Sn–O^<i>i</i>Pr across a CC Bond: Unusual Insertion of an Alkene into a Main-Group-Metal–Alkoxide Bond

An example of unusual addition of a main-group-metal alkoxide across an alkene CC bond was demonstrated with a dimethylvinylsilyl-substituted Sn-POSS complex (POSS = incompletely condensed polyhedral oligomeric silsesquioxane). The structure of the pentacoordinated Sn chelate product was confirmed by ¹H, ¹³C, and ¹¹⁹Sn NMR and ESI-MS

Selective Hydrodeoxygenation of Guaiacol to Phenolics by Ni/Anatase TiO2 Catalyst Formed by Cross-Surface Migration of Ni and TiO2

The catalytic properties of physical mixtures of Ni particles (100-200 nm) with nanoparticles of anatase TiO2 (TiO2-A), ZrO2, Al2O3, rutile TiO 2 (TiO2-R), and CeO2 were investigated for the hydrodeoxygenation (HDO) of guaiacol. High selectivities to phenolics were obtained only for Ni mixed with anatase TiO2 (Ni and TiO2-A), while saturated hydro- carbons were the main products for the mixtures with other supports. By thermal treatment in hydrogen gas only at 300 degrees C or higher and subsequently separating the large Ni particles from the TiO2-A particles with a magnet, it was further discovered that there was migration of TiO 2 from TiO2-A onto the large Ni particles, resulting in an amorphous TiO2 overlayer on the Ni particles as evidenced by high-resolution TEM, and vice versa, migration of Ni onto TiO2-A. The TiO2 overlayer rendered the Ni particles completely inactive as a hydrogenation/hydrodeoxygenation catalyst. Conversely, the small amounts of Ni (<1.5 wt %) migrated onto TiO2-A formed highly dispersed Ni, undetectable by high-resolution TEM (<2 nm), that were remarkably highly active for HDO of guaiacol, producing selectively phenolics. Such highly selective HDO catalysts could also be formed by incipient wetness impregnation of Ni in loadings above 2 wt % onto the TiO2-A, but it was essential to pretreat the sample in H-2 at 300 degrees C or higher. Pretreatment in H-2 at 200 degrees C generated catalysts that produced saturated ring products. The activity of the impregnated catalysts, as measured by guaiacol conversion, increased linearly with Ni loading below 0.5 wt %. The activity continued to increase with Ni loading but more slowly up to 2 wt %, beyond which there was little further change. The results suggested that two types of Ni species existed on the TiO2-A surface. One type consisted of a cluster of Ni atoms that were dominant on larger Ni particles that were active in aromatic ring hydrogenation and hydrodeoxygenation. They were readily covered by reducible TiO2-A at 300 degrees C or higher due to the traditional strong metal support interaction (SMSI) effect and became inactive. Another type was clusters of a very small number of Ni atoms, perhaps one atom, that were present as highly dispersed Ni clusters interacting strongly with the defect sites of TiO2-A. The strong interaction of this type of Ni with the TiO2 defect deterred TiO, migration allowing surface exposed Ni atoms to catalyze the HDO of guaiacol with very high selectivities that were not characteristic of typical Ni particles

Generating and Stabilizing Co(I) in a Nanocage Environment

A discrete nanocage of core–shell design, in which carboxylic acid groups were tethered to the core and silanol to the shell interior, was found to react with Co₂(CO)₈ to form and stabilize a Co­(I)–CO species. The singular CO stretching band of this new Co species at 1958 cm^–1 and its magnetic susceptibility were consistent with Co­(I) compounds. When exposed to O₂, it transformed from an EPR inactive to an EPR active species indicative of oxidation of Co­(I) to Co­(II) with the formation of H₂O₂. It could be oxidized also by organoazide or water. Its residence in the nanocage interior was confirmed by size selectivity in the oxidation process and the fact that the entrapped Co species could not be accessed by an electrode