Three factors, (i) the ethanol “blend wall”, which limits its market as a transportation fuel, (ii) advances in production efficiency, and (iii) feedstock diversification, could lead to excess ethanol at competitive prices. Those factors have already motivated a search for value-added derivatives (e.g., distillate fuels, olefins, and asymmetric amines). Siting small, low cost, flexible conversion facilities to process ethanol at or near the fermentation plant could encourage the growth of an enterprise. Decreasing the barriers to entry, matching supply and demand, and enhancing access to production incentives are enabling success factors. This review discusses the process chemistries that might be employed by such ethanol conversion facilities based on market prices. Then, we describe how these technologies might benefit from process intensification to simplify the processing and to avoid large pressures or large temperature gradients typically employed in conventional, large scale facilities.

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Ethanol is a promising platform molecule for production of a variety of fuels and chemicals. Of particular interest is the production of middle distillate fuels (i.e., jet and diesel blendstock) from renewable ethanol feedstock. State-of-the-art alcohol-to-jet technology requires multiple process steps based on the catalytic dehydration of ethanol to ethylene, followed by a multistep oligomerization including n-butene formation and then hydrotreatment and distillation. Here we report that, over Ag-ZrO2/SBA-16 with balanced metal and Lewis acid sites, ethanol is directly converted to n-butene (1- and 2-butene mixtures) with an exceptional butene-rich olefin selectivity of 88% at 99% conversion. The need for the ethanol dehydration to ethylene step is eliminated. Thus, it offers the potential for a reduction in the number of required processing units versus conventional alcohol-to-jet technology. We also found that the C4 product distribution, n-butene and/or 1,3-butadiene, can be tailored on this catalyst by tuning the hydrogen feed partial pressure and other process/catalyst parameters. With sufficient hydrogen partial pressure, 1,3-butadiene is completely and selectively hydrogenated to form n-butene. The reaction mechanism was elucidated through operando-nuclear magnetic resonance investigations coupled with reactivity measurements. Ethanol is first dehydrogenated to acetaldehyde over the metallic Ag, then acetaldehyde is converted to crotonaldehyde over the acid sites of ZrO2/SiO2 via aldol condensation followed by dehydration. This is followed by a Meerwein–Ponndorf–Verley reduction of crotonaldehyde to butadiene intermediate that is hydrogenated into n-butene over metallic Ag and ZrO2. A minor fraction of n-butene is also produced from crotonaldehyde reduction to butyraldehyde instead of butadiene. Isotopically labeled ethanol NMR experiments demonstrated that ethanol, rather than H2, is the source of H for the hydrogenation of crotonaldehyde to butyraldehyde. Combined experimental-computational investigation reveals how changes in silver and zirconium composition and the silver oxidation state affects reactivity under controlled hydrogen partial pressures and after prolonged run times. Finally, catalyst effectiveness also was demonstrated when using wet ethanol feed, thus highlighting process flexibility in terms of feedstock purity requirements.

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Muscovite mica (001) is a widely used model surface for controlling molecular assembly and a common substrate for environmental adsorption processes. The mica (001) surface displays near-trigonal symmetry, but many molecular adsorbatesincluding waterexhibit unequal probabilities of alignment along its three nominally equivalent lattice directions. Buried hydroxyl groups within the muscovite structure are speculated to be responsible, but direct evidence is lacking. Here, we utilize vibrational sum frequency generation spectroscopy (vSFG) to characterize the orientation and hydrogen-bonding environment of near-surface hydroxyls inside mica. Multiple distinct peaks are detected in the O–H stretch region, which we attribute to Si/Al substitution in the SiO4 tetrahedron and K+ ion adsorption above the hydroxyls based on density functional theory simulations. Our findings demonstrate that vSFG can identify the absolute orientation of −OH groups and, hence, the surface termination at a mica surface, providing a means to investigate how −OH groups influence molecular adsorption and better understand mica stacking-sequences and physical behavior.

Ag−ZrO2/SBA‐16 has recently been found to be efficient for catalyzing the single‐step conversion of ethanol to butene (1‐ and 2‐butene mixtures) in the presence of H2. The reaction proceeds via a cascading sequence of reactions over mixed metal and Lewis sites, with the catalyst composition tuned to selectively favor butene formation. However, the catalyst slowly deactivates when evaluated over long reaction times. In this work, we evaluated the lifetime of the Ag−ZrO2/SBA‐16 catalyst system for ethanol‐to‐butene conversion at 325 °C for up to 800 hours on stream. Several characterization techniques were used to elucidate the mechanism(s) by which catalyst deactivation occurs. Coke deposition, Ag particle sintering, and Ag0‐to‐Ag+ oxidation state change were identified to be the major causes of catalyst deactivation. Coke deposits cover primarily Lewis acid sites which are responsible for aldol condensation, Meerwein‐Ponndorf‐Verley (MPV) reduction, and dehydration reactions. Ag particle sintering and Ag oxidation state change leads to a reduction in the number of metallic Ag sites responsible for the dehydrogenation/hydrogenation steps. The fresh catalyst likely experiences hydrothermal sintering in the early stage of reaction and permanently loses some active Lewis acid sites before reaching a new structural steady state. The deactivation of Lewis acid sites leads to a decrease in overall ethanol conversion, whereas the deactivation of the metallic Ag sites decreases the butene selectivity. For catalyst regeneration, oxidative calcination (at 500 °C) followed by reduction (at 325 °C) successfully removes all the coke species on the catalyst surface and restores the metallic Ag particles of the 4Ag−4ZrO2/SBA‐16 catalysts.

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