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Due to a set of unique properties, carbon materials are applied as supports for metal-based catalysts in a wide variety of established and emerging (electro-)catalytical transformations. By introducing heteroatoms such as N, S and P into carbon supports, metal-support interactions can be tuned, enabling an optimization of catalyst performance in terms of activity, selectivity and stability. However, the exact impact of carbon heteroatom doping on catalyst performance remains often poorly understood, as the effects are inseparable from the clustered influence of other support properties such as texture and nanostructure. In this context, we present gasification-assisted heteroatom doping (GAHD) as a novel, broadly applicable post synthesis approach to exchange carbon surface atoms against heteroatoms while retaining the properties of the parental carbon. Employing GAHD, N, S and P doping of carbons with widely varying properties could be achieved, allowing, for example, incorporation of up to 13.1 wt-% S into an activated carbon at a change of specific surface area of only 4.4%. As a proof-of-concept, comparable N, S and P doped carbon nanofiber supports were used to prepare Pt-based electrocatalysts for the oxygen reduction reaction and probe the influence of the heteroatom dopants on their stability by accelerated stress tests in different potential regimes. In this context, P and S doped supports were found to exhibit a high degree of interaction with Pt, providing increased degradation resistance compared to N and non-doped support.

Due to their chemical and thermal stability, electrical conductivity, and high specific surface areas, nanocarbons and porous carbon materials have found use in numerous key applications within the current transition of energy and raw-material sources. Since all these applications rely on multiphase interactions between the carbon surface and surrounding solid, liquid, or gaseous phases, carbon surface chemistry is elevated to a critical factor of influence. However, the characterization of carbon surface chemistry is notoriously complex, involving carbon defect sites and chemically similar heteroatom species in a wide range of different binding states and chemical environments. Due to this high degree of complexity, a comprehensive characterization of carbon surface species and reactivity is a major challenge for which there is no analytical “silver bullet” but is fundamental to the rational development of advanced functional carbon materials. In this context we would like to highlight the potential of temperature-programmed techniques (TPX) for carbon surface analytics, which benefit from widely available, easy-to-handle equipment and offer information on the identity, quantity, and reactivity of surface species. Hence, this article reviews the state of the art concerning temperature-programmed techniques for carbon surface characterization, focusing not only on the qualitative and quantitative analysis of carbon surface species but also on the unique ability of temperature-programmed methods to assess carbon surface reactivity. In this context, progress made so far in temperature-programmed desorption, temperature-programmed reduction, and temperature-programmed surface reactions is discussed, highlighting pitfalls and gaps in knowledge. Based on this foundation, strategies for the further development of temperature-programmed methods for carbon surface analysis are proposed, aiming to establish TPX as the future gold-standard in carbon surface characterization.

Aqueous phase reforming (APR) of ethylene glycol was performed at 225 °C and 30 bar in batch and continuous reaction conditions. The effect on the APR performance by functionalizing carbon supports with nitrogen and adding Mn to Pt-based catalysts was investigated. The presence of nitrogen species on the carbon surface and Mn-addition (PtMn) improved the catalytic activity and promoted H2 production. XPS results suggest that the enhancement of the catalytic activity may be attributed to charge transfer from platinum to the nitrogen groups and Mn. Pt-based catalysts were stable under the studied reaction conditions, while up to 97 % of the manganese leached into the liquid solution during APR. However, the catalytic activity was maintained even with such significant decrease in Mn content, indicating that only a small amount of Mn is necessary to maintain the promotional effect on Pt during APR.

Manipulation of carbon surface functionalization and especially of oxygen surface groups has been demonstrated to be key for obtaining high performance materials in a multitude of applications. Although control of carbon surface chemistry offers large potential in many technical relevant applications, qualitative and quantitative analysis of surface oxides for amorphous and porous carbons remains challenging. In this study, we attempt selective, organic chemistry-based functionalization of a polymer-derived porous model carbon featuring high oxygen loadings, with the aim to establish analytical standards for temperature programmed desorption (TPD) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). In this context, quantitative chemical reduction of an oxidized carbon material with lithium aluminum hydride (LiAlH4) is utilized as the key for the synthesis of carbon materials with defined ensembles of oxygen surface groups (hydroxyl groups and ethers). Based on this reduction strategy, selective LiAlH4 reduction based on protection group chemistry leads to aldehydes, ketones and quinones as surface functional groups and chemical grafting is studied for the selective introduction of phenyl esters, methyl ethers and carboxylic acids. All materials are evaluated with respect to the applicability as analytical standard by DRIFT spectroscopy, TPD, X-ray photoelectron spectroscopy and titration methods.

Catalytic conversion of n-butanol to high-value-added product is considered as a highly important route towards biomass derived fine chemicals. The present work reports the applications of non-metallic multi-walled carbon nanotube (CNT) as bifunctional catalysts for oxygen assisted n-butanol conversion reactions. Oxidative dehydrogenation (ODH) and dehydration of n-butanol on CNT yielded aldehyde and alkene compounds via redox and acid catalytic routes, respectively. CNT exhibited high activity (over 50% n-butanol conversion) and stability (over 120 h) under gentle reaction conditions (

Methanol dehydrogenation to formaldehyde or dehydration to dimethyl ether are high-value-added industrial processes. Here, we applied oxidized multi-walled carbon nanotubes (oCNTs) in a methanol conversion reaction in the presence of oxygen. oCNT catalysts exhibit a methanol conversion of 60% under gentle reaction conditions, yielding DME (65%) and FA (30%) as the main products, and long term stability for over 150 h is achieved. The catalytic performance of oCNTs is even comparable to industrial metal catalysts. An in situ site titration experiment revealed that carboxyl groups were the active sites for the formation of dimethyl ether. Small organic molecules as model catalysts suggested that quinoidic carbonyl groups may be responsible for methanol ODH producing formaldehyde, while both quinoidic and ketonic carbonyl groups are responsible for total oxidation to carbon dioxide. Basic reaction kinetics and mechanisms such as reaction orders, apparent activation energy, rate determining step, etc. for the oxidative dehydrogenation and dehydration of methanol were studied systematically. A unique gentle redox catalytic activity of oCNT catalysts could be realized to reduce the overoxidation losses.

Until now, oxygen functionalized carbon materials were not considered to exhibit significant acidity at high temperatures, since carboxylic acids, the most prominent acidic functionality, are prone to decarboxylation at temperatures exceeding 250 °C. Paradoxically, we could show that oxidized carbon materials can act as highly active high‐temperature solid acid catalysts in the dehydration of methanol at 300 °C, showing an attractive selectivity to dimethyl ether (DME) of up to 92 % at a conversion of 47 %. Building on a tailor‐made carbon model material, we developed a strategy to utilize in situ DRIFT spectroscopy for the analysis of carbon surface species under process conditions, which until now proofed to be highly challenging due to the high intrinsic absorbance of carbon. By correlating the catalytic behavior with a comprehensive in situ DRIFTS study and extensive post mortem analysis we could attribute the high‐temperature acidity of oxidized carbons to the interaction of thermally stable carboxylic anhydrides and lactones with nucleophilic constituents of the reaction atmosphere e. g. methanol and H₂O. Dynamic equilibria of surface oxides depending on reaction atmosphere and temperature were observed, and a methyl ester, formed by methanolysis of anhydrides and lactones, was identified as key intermediate for DME generation on oxidized carbon catalysts.

Poisson processes in the space of $$(d-1)$$ ( d - 1 ) -dimensional totally geodesic subspaces (hyperplanes) in a d-dimensional hyperbolic space of constant curvature $$-1$$ - 1 are studied. The k-dimensional Hausdorff measure of their k-skeleton is considered. Explicit formulas for first- and second-order quantities restricted to bounded observation windows are obtained. The central limit problem for the k-dimensional Hausdorff measure of the k-skeleton is approached in two different set-ups: (i) for a fixed window and growing intensities, and (ii) for fixed intensity and growing spherical windows. While in case (i) the central limit theorem is valid for all $$d\ge 2$$ d ≥ 2 , it is shown that in case (ii) the central limit theorem holds for $$d\in \{2,3\}$$ d ∈ { 2 , 3 } and fails if $$d\ge 4$$ d ≥ 4 and $$k=d-1$$ k = d - 1 or if $$d\ge 7$$ d ≥ 7 and for general k. Also rates of convergence are studied and multivariate central limit theorems are obtained. Moreover, the situation in which the intensity and the spherical window are growing simultaneously is discussed. In the background are the Malliavin–Stein method for normal approximation and the combinatorial moment structure of Poisson U-statistics as well as tools from hyperbolic integral geometry.

A new strategy affords “non‐nano” carbon materials as dehydrogenation catalysts that perform similarly to nanocarbons. Polymer‐based carbon precursors that combine a soft‐template approach with ion adsorption and catalytic graphitization are key to this synthesis strategy, thus offering control over macroscopic shape, texture, and crystallinity and resulting in a hybrid amorphous/graphitic carbon after pyrolysis. From this intermediate the active carbon catalyst is prepared by removing the amorphous parts of the hybrid carbon materials via selective oxidation. The oxidative dehydrogenation of ethanol was chosen as test reaction, which shows that fine‐tuning the synthesis of the new carbon catalysts allows to obtain a catalytic material with an attractive high selectivity (82 %) similar to a carbon nanotube reference, while achieving 10 times higher space–time yields at 330 °C. This new class of carbon materials is accessible via a technically scalable, reproducible synthetic pathway and exhibits spherical particles with diameters around 100 μm, allowing unproblematic handling similar to classic non‐nano catalysts., An amorphous/graphitic hybrid material is synthesized by growing nanoscale graphite crystallites in a non‐nano polymer‐derived carbon by catalytic graphitization. An active dehydrogenation catalyst is obtained by creating accessibility to these graphitic domains via selective oxidation. This carbon dehydrogenation catalyst offers a 10‐fold increase in space‐time‐yield in the oxidative dehydrogenation of ethanol compared to a carbon nanotube benchmark.

Eine neue Synthesestrategie liefert “Nicht-nano”-Kohlenstoffmaterialien als Dehydrierungskatalysatoren, die eine ähnliche katalytische Leistung wie Nanokohlenstoffe aufweisen. Schlüsselelement sind hierbei Kohlenstoffpräkursoren auf Polymerbasis, die eine Soft-Templat-Strategie mit Ionenadsorption und katalytischer Graphitisierung kombinieren, um eine Kontrolle der makroskopischen Form, Textur und Kristallinität zu ermöglichen und nach der Pyrolyse einen hybriden amorph/graphitischen Kohlenstoff zu erhalten. Aus diesem Zwischenprodukt wird der aktive Kohlenstoffkatalysator hergestellt, indem die amorphen Anteile des Hybridkohlenstoffs durch selektive Oxidation entfernt werden. Die oxidative Dehydrierung von Ethanol wurde als Testreaktion gewählt. Die neuen Kohlenstoffkatalysatoren zeigen eine vergleichbar hohe Selektivität (82 %) wie ein Benchmark mit Kohlenstoffnanoröhren, jedoch mit 10-mal höheren Raum-Zeit-Ausbeuten bei 330 °C. Diese neuartigen Kohlenstoffmaterialien sind über einen technisch skalierbaren, reproduzierbaren Syntheseweg zugänglich und weisen kugelförmige Partikel mit Durchmessern um 100 μm auf, was eine unproblematische Handhabung ermöglicht.

The nature of methanol conversion on borocarbonitride was revealed via active site quantification and kinetic analysis., Borocarbonitrides (BCNs) have emerged as highly selective catalysts for the oxidative dehydrogenation (ODH) reaction. However, there is a lack of in-depth understanding of the catalytic mechanism over BCN catalysts due to the complexity of the surface oxygen functional groups. Here, BCN nanotubes with multiple active sites are synthesized for oxygen-assisted methanol conversion reaction. The catalyst shows a notable activity improvement for methanol conversion (29%) with excellent selectivity to formaldehyde (54%). Kinetic measurements indicate that carboxylic acid groups on BCN are responsible for the formation of dimethyl ether, while the redox catalysis to formaldehyde occurs on both ketonic carbonyl and boron hydroxyl (B─OH) sites. The ODH reaction pathway on the B─OH site is further revealed by in situ infrared, x-ray absorption spectra, and density functional theory. The present work provides physical-chemical insights into the functional mechanism of BCN catalysts, paving the way for further development of the underexplored nonmetallic catalytic systems.

Carbon surface oxides have been demonstrated to be crucial for high performing carbon materials in various applications. Diffuse reflectance infrared Fourier transform spectroscopy represents a powerful time-resolved method to study the surfaces of functional materials under process conditions. Due to the severe overlap of the contributions of individual surface groups in combination with compared to organic molecules shifted absorption maxima meaningful analysis remains challenging. Especially due to the unknown maxima, deconvolution of the superimposed bands is strongly hindered. In this study, we developed a procedure based on hydrolysis, thermal annealing or a combination thereof, which allows to disentangle carbonyl absorption maxima of carboxylic acids, anhydrides and lactones on carbon surfaces. In order to verify the proposed transformations, thorough characterization by temperature programmed desorption, X-ray photoelectron spectroscopy, potentiometric titration and Boehm titration was carried out. Applying this procedure for a polymer derived reference material, the carbonyl absorption maximum could be deduced, which are positioned for lactones at 1771 cm−1, for carboxylic acids between 1753 cm−1 and 1760 cm−1, and for carboxylic anhydrides at 1792 cm-1 and 1852 cm-1. This allowed deconvolution of the carbonyl band, paving the way for in situ time-resolved analyses.

Kinetic analysis is a powerful and effective strategy to reveal the physical-chemical nature of the promotion effect of heteroatoms to nanocarbon catalysts. The present work reported the mechanistic and kinetic analysis of ethylbenzene oxidative dehydrogenation (ODH) reactions on heteroatom (N or B) doped and undoped carbon nanotube (CNT) catalysts via active site titration, kinetic isotope effect and single reactant surface reaction experiments etc. The physical-chemical meanings behind the elementary step rate and equilibrium constants were revealed and applied for interpretations of the promotion effect of heteroatoms at molecular level. Nitrogen doped CNT exhibited both higher rate and equilibrium constants for C–H bond dissociation and O2 adsorption than undoped one via facilitating the electron transfer process. The evolution of the active sites could be quantitatively described with rate equation via the theory of most abundant surface intermediates, which provides in depth understandings on the mechanism and structure-function relations in carbon catalyzed redox reactions.