Propene ammoxidation to acrylonitrile (ACN) over bismuth molybdate-based catalysts has been commercialized for more than 60 years. To meet forecasted growth, there is an opportunity for smaller-scale, decentralized ACN production. Forced dynamic operation (FDO), here referring to step changes in reactant inlet concentrations, has been used in low-volume production applications and has shown advantages in partial oxidation reactions. As a proof-of-concept study to evaluate FDO for acrylonitrile production, we applied periodic changes in inlet gas concentrations that varied between one phase containing all reactants and another that just contained O2, over an industrial bismuth molybdate-based catalyst. We varied the cycle period, duty cycle, and O2 concentration in the second phase and show that improved acrylonitrile yields can be obtained compared with those of steady-state operation under certain conditions. A correlation between lattice oxygen availability and FDO performance was observed.

Research into the incorporation of cerium into a diverse range of catalyst systems for a wide spectrum of process chemistries has expanded rapidly. This has been evidenced since about 1980 in the increasing number of both scientific research journals and patent publications that address the application of cerium as a component of a multi-metal oxide system and as a support material for metal catalysts. This review chronicles both the applied and fundamental research into cerium-containing oxide catalysts where cerium's redox activity confers enhanced and new catalytic functionality. Application areas of cerium-containing catalysts include selective oxidation, combustion, NOx remediation, and the production of sustainable chemicals and materials via bio-based feedstocks, among others. The newfound interest in cerium-containing catalysts stems from the benefits achieved by cerium's inclusion, which include selectivity, activity, and stability. These benefits arise because of cerium's unique combination of chemical and thermal stability, its redox active properties, its ability to stabilize defect structures in multicomponent oxides, and its propensity to stabilize catalytically optimal oxidation states of other multivalent elements. This review surveys the origins and some of the current directions in the research and application of cerium oxide-based catalysts.

•Some of the highest experimental yields (>70 wt. %) of glycolaldehyde achieved and reported to date.•Good agreement between model and experimental results.•Dominant fragmentation pathways elucidated in hydrothermal pyrolysis of glucose.•Preferred operating conditions and feedstock sugar identified toward maximum glycolaldehyde production.

Taurine, 2-aminoethane-1-sulfonic acid, is a commercial amino acid manufactured from either ethylene oxide or monoethanolamine (MEA). Taurine is a valuable nutritional additive that is widely used in the production of energy drinks, pet food, nutritional supplements, and infant formula. The industrial production of taurine from MEA is a two-step batch process in which the first step is the reaction of MEA with sulfuric acid to produce the ester 2-aminoethyl hydrogen sulfate (AES) and the second step is the reaction of AES with a sulfite reagent. This report summarizes the results of a study of the fundamental chemistry for this two-step MEA-based chemical route to taurine as well as the application of this fundamental understanding to a process design for a scalable and cost-advantaged continuous process that is capable of commercial-scale production of taurine on a multikiloton scale. In order to maximize taurine yields, the water formed during the first esterification step must be effectively removed to avoid equilibrium limitations on the conversions of MEA and sulfuric acid to form the solid AES intermediate product. For the second AES sulfonation step in aqueous medium, we found that operation above 100 degrees C under a moderate pressure of an inert gas resulted in significantly higher taurine yields (>80 mol %) compared to those reported in current commercial production technology (typically 55-65 mol %).

This contribution is a brief technology retrospective but mostly a look forward at the trajectory of technology development for the manufacture of acrylonitrile. An analysis is presented for the criteria that would enable the displacement of the current dominant commercial SOHIO Process for selective propylene ammoxidation catalysis. These criteria reveal that significant opportunity exists for both fundamental and applied research directed toward the design of new catalysts for the current commercially dominant propylene ammoxidation process but also for novel catalysts that can enable the use of lower cost feedstocks for acrylonitrile manufacture. These feedstocks include propane and biomass derived sources. The ability to retrofit a new catalyst technology into existing propylene ammoxidation plant infrastructure is likely key to achieve displacement cost advantage of the magnitude that was realized by propylene ammoxidation catalysis decades earlier.

Multifunctionality is the hallmark of most modern commercial heterogeneous catalyst systems in use today, including those used for the selective ammoxidation of propylene to acrylonitrile. It is the quintessential principle underlying commercial catalyst design efforts since petrochemical process development is invariably driven by the need to reduce manufacturing costs. This is in large part achieved through new and improved catalysts that increase selectivity and productivity. In addition, the future feedstocks for chemical processes will be invariably more refractory than those currently in use (e.g., replacing alkenes with alkanes or using CO2), thus requiring a disparate combination of chemical functions in order to effect multiple chemical transformations with the fewest separate process steps. This review summarizes the key chemical phenomena behind achieving the successful integration of multiple functions into a mixed-metal-oxide-selective ammoxidation catalyst. An experiential and functional catalyst design model is presented that consists of one or both of the following components: (1) a mixed-metal-oxide–solid solution where the individual metal components serve separate and necessary functions in the reaction mechanism through their atomic level interaction in the context of a single crystallographic structure; (2) the required elemental components and their catalytic function existing in separate phases, where these phases are able to interact for the purposes of electron and lattice oxygen transfer through the formation of a structurally coherent interface (i.e., epitaxy) between the separate crystal structures. Examples are provided from the literature and explained in the context of this catalyst design model. The extension of the model concepts to the design of heterogeneous catalysts in general is also discussed.

The objective of this article is to use the example of the development of metal oxide catalysts for the selective ammoxidation and oxidation of propylene to illustrate successful catalyst design strategies for achieving enhanced yields of acrylonitrile and acrolein, respectively. The processes of catalytic selective ammoxidation and oxidation of propylene are not the only, albeit they are among the most industrially significant, examples of the commercial application of metal oxide selective oxidation catalysts. Other important commercial catalytic processes that use highly developed metal oxide catalysts systems include butane oxidation to maleic anhydride and alkyl aromatic ammoxidation of toluene, xylenes, and picolines (alkyl pyridines) to produce valuable aromatic nitriles including nicotinonitrile which is the precursor for nicotinic acid (niacin) an important B-complex vitamin. Using the example of industrial propylene selective (amm)oxidation, this article surveys the available patents, scientific and technical journals to chronical and analyze the development and advancement of the complex metal oxides from discovery to current state-of-the-art. Recognizing that commercial practices are proprietary, this analysis uses no known company sensitive or confidential information is included in these descriptions. From this analysis a comprehensive catalyst design strategy unfolds that is based on the enabling science of solid state chemistry and the results of the characterization tools it provides. This provides a viable platform to unlock the next level of metal oxide catalyst development with ultra-high selectivity for hydrocarbon oxidation.

The scheelite (CaWO4) structure type serves as the framework for a wide variety of metal oxide catalysts used for the selective oxidation and ammoxidation of alkenes.

Acrylonitrile is a major chemical intermediate used in the production of a wide range of chemical and polymer products. Central to the commercial process is a proprietary catalyst consisting of a complex mixture of metal oxides containing a bismuth-containing molybdate phase that is active and selective for propylene ammoxidation to acrylonitrile. Among the most active and selective is a solid solution of bismuth and cerium molybdate. Solid state structural studies were undertaken to characterize this active phase. The results show that the mixed bismuth cerium molybdate consists of a solid solution phase having the scheelite-related structure of cerium molybdate with a monoclinic unit cell. Analysis of the cation site occupancy using synchrotron X-ray diffraction indicates that bismuth preferentially occupies the Ce(3) site of the monoclinic cerium molybdate structure. It is therefore possible to singularly identify the structure of the active site for propylene ammoxidation given that bismuth is a necessary constituent of a site for selective propylene (amm)oxidation. The proposed active site consists of bismuth located next to a cation vacancy in the structure, presumably in order to accommodate its lone pair of electrons. Bismuth serves as the site for the rate determining alpha-hydrogen abstraction from propylene to form an allyl intermediate and subsequent nitrogen insertion and loss of lattice oxygen. The bismuth site is surrounded by two cerium cations in this active site configuration. Thus the model that emerges from this study is Bi3+ and Ce3+ in a molybdate structural framework with cerium readily able to undergo Ce3+ <-> Ce4+ redox that facilitates lattice oxygen transfer to the active site as required by the operative Mars van Krevelen mechanism for selective propylene ammoxidation. The presence of two cerium cations adjacent to bismuth as a key component of the active site is expected to promote the rapid re-oxidation of the catalytic site effecting enhanced catalytic performance with respect to selective product yields and productivity. (C) 2015 Elsevier B.V. All rights reserved.