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Electrification to reduce or eliminate greenhouse gas emissions is essential to mitigate climate change. However, a substantial portion of our manufacturing and transportation infrastructure will be difficult to electrify and/or will continue to use carbon as a key component, including areas in aviation, heavy-duty and marine transportation, and the chemical industry. In this Roadmap, we explore how multidisciplinary approaches will enable us to close the carbon cycle and create a circular economy by defossilizing these difficult-to-electrify areas and those that will continue to need carbon. We discuss two approaches for this: developing carbon alternatives and improving our ability to reuse carbon, enabled by separations. Furthermore, we posit that co-design and use-driven fundamental science are essential to reach aggressive greenhouse gas reduction targets.

Mesoporous silicas such as SBA-15 and MCM-41 are investigated for potential applications in catalysis, separations, and the synthesis of nanostructured materials. Pyrolysis of the silica-immobilized DPP reveals that pore confinement leads to enhanced rates and altered product selectivities also depend on pore size.

Pyrolysis of silica-immobilized 1,3-diphenylpropane (DPP) is examined in the presence of a series of isomeric co-attached hydroaromatic spacer molecules to explore the role of molecular orientation on a free-radical reaction under surface confinement. The DPP pyrolysis rate is found to be sensitive to both the structure of the spacer and its attachment orientation to the surface.

Research describes the flash vacuum pyrolysis of methoxy-substituted beta-O-4 lignin compounds at 500 C, which involves free-radical reactions, molecular rearrangements, and elimination reactions. Data discuss the reactions with model lignin compounds.

The pyrolysis of silica-immobilized benzyl phenyl ether (BPE) at 275 to 375 degrees C has been examined. The study seeks to find out the impact of restricted mass transport on the pyrolysis mechanism compared with previous studies in fluid phases. Results reveal significant altered product distribution due to restricted mass transport compared with corresponding studies of BPE in fluid phases. The dominant products originate from two rearrangement pathways even if pyrolysis is initiated by the homolytic scission of the O-C bond to form phenoxy and benzyl radicals.

A new chemical/spectroscopic couple that differentiates aromatic from aliphatic carboxylic acid polymers was developed. The method is complementary to more traditional methods of identification (IR) and is applicable to the analysis of complex mixtures where IR determinations are complicated by extensive vibrational band overlap. The method entails (1) conversion of carboxylic acids into acid fluorides and (2) specific detection of the resonances of the acid fluoride carbon and of the carbon directly attached to the carbonyl carbon by solid state 19F-13C cross polarization (CP)/MAS 13C NMR. The assignment of the chemical shift of the latter resonance to either the [sp.sup.2] or [sp.sup.3] carbon resonance manifold specifies the nature of the acid functionality. The preparation of the acid fluoride derivatives of several polymers containing aliphatic and aromatic carboxylic acid functionality was evaluated using sulfur tetrafluoride ([SF.sub.4]), diethylaminosulfur trifluoride (DAST), cyanuric fluoride, and thionyl fluoride. Room temperature reactions using DAST in methylene chloride or neat S[F.sub.4] gave the acid fluorides in yields [greater than or equal to]90% for the acids studied. Aromatic acid fluoride yields were essentially quantitative. Aliphatic acid fluorides were contaminated with the anhydride of the acid. The acid fluoride polymers were characterized by solid state 13C and 19F MAS/NMR.

Immobilized organic compounds on silica surfaces were examined to determine the effects of restricted mass transport on high-temperature, free radical reactions. Thermolysis of the immobilized compounds was done with different coattached spacer molecules and generated toluene and styrene as principal products. Rate improvements were attributed to a novel hydrogen transfer, radical relay mechanism.

A study of the thermolysis of phenethyl phenyl ether (PPE) at 330-425 degree celsius, is conducted to mitigate the discrepancies in the mechanisms of this model of the ether linkages, in lignin and low rank coal. The scission of PPE occurs through alpha/beta selectivity resulting in the formation of styrene plus phenol, and benzaldehyde plus toluene. Styrene and phenol are produced by hydrogen abstraction at the alpha-carbon, while benzaldehyde and toluene are formed by hydrogen abstraction at the beta-carbon.

The overall [alpha]/[beta]-selectivity is calculated for the pyrolysis of phenethyl phenyl ether as a composite of the [alpha]/[beta]-selectivites in the hydrogen abstraction reactions by the phenoxyl and by the benzyl radical. Quasi-steady-state kinetic analysis is used for the intermediate radicals in order to obtain the composite [alpha]/[beta]-product selectivity.

In heterogeneous catalysis, hydrides on the surface or in the bulk play a critical role as either active components or reaction intermediates in many hydrogen‐involving reactions, but characterization of the nature and structure of these hydride species remains challenging. Neutron scattering, which is extremely sensitive to light elements, such as hydrogen, has shown great potential in meeting this challenge. In this Minireview, recent advances in neutron studies of hydride species, mainly over the two most typical classes of catalysts—metals and oxides—are surveyed. Findings on catalysts outside these categories are raised if they are considered to be relevant for contextualization in the present Minireview. The adsorption, dissociation, spillover, and reactivity of hydrogen, especially hydride species over supported metal and oxide catalysts, have been successfully investigated, mostly by means of neutron vibrational spectroscopy. Insights from these neutron studies, which are otherwise not possible with other techniques, shed light on the interaction mechanism of hydrogen with solid surfaces and reaction mechanisms in which hydrogen is involved. Future research challenges on neutron scattering studies of hydrides, as well as catalysis in general, are also highlighted, and more operando‐type neutron studies need be conducted to advance the field. Suitable surfaces: In heterogeneous catalysis, hydrides play a critical role in many hydrogen‐involving reactions. Neutron scattering has the unique potential to characterize hydrides. Herein, recent advances in neutron studies of hydride species over supported metal and oxide catalysts are reviewed. [ABSTRACT FROM AUTHOR]

Even subtle changes in molecular orientation can have a significant effect on the rate of the hydrogen transfer, radical relay process, a finding that has much broader implications for bimolecular reactions occurring on surfaces under restricted diffusion. The results of a study indicate that a meta-orientation for the surface linkage with respect to the reactive benzylic hydrogens, provides the most efficient geometry for promoting the hydrogen transfer, radical relay process on the surface.