Co-reporter:Florian Göltl, Carine Michel, Prokopis C. Andrikopoulos, Alyssa M. Love, Jürgen Hafner, Ive Hermans, and Philippe Sautet
ACS Catalysis December 2, 2016 Volume 6(Issue 12) pp:8404-8404
Publication Date(Web):November 17, 2016
DOI:10.1021/acscatal.6b02640
Transition metal-oxo centers in zeolites are known to be active in the conversion of methane to methanol. Here, we study this reaction over Fe-oxo sites in the zeolite SSZ-13. By comparing calculations for the fully periodic structure and a cluster for two different methods—the standard van der Waals corrected semilocal density functional PBE-D2 and ACFDT-RPA, which is a method where correlation is calculated fully nonlocally—we find that it is actually the confining environment in the zeolite that reduces the barrier for this reaction, by more than 50%, and we find that the two applied methods lead to qualitatively different results.Keywords: ACFDT-RPA; confinement effects; density functional theory; methane; methanol; zeolites;
Co-reporter:Florian Göltl, Philipp Müller, Pajean Uchupalanun, Philippe Sautet, and Ive Hermans
Chemistry of Materials August 8, 2017 Volume 29(Issue 15) pp:6434-6434
Publication Date(Web):July 10, 2017
DOI:10.1021/acs.chemmater.7b01860
The discovery of new materials tailored for a given application typically requires the screening of a large number of compounds, and this process can be significantly accelerated by computational analysis. In such an approach the performance of a compound is correlated to a materials property, a so-called descriptor. Here we develop a descriptor-based approach for the adsorption of CO and NO to Cu, Ni, Co, and Fe sites in zeolites. We start out by discussing a possible design strategy for zeolite catalysts, define the studied test set of sites in the zeolites SSZ-13 and mordenite, and define a set of appropriate descriptors. In a subsequent step we use these descriptors in single-parameter, two-parameter, and multiparameter regression analysis and finally use a machine-learning genetic algorithm to reduce the number of variables. We find that one or two descriptors are not sufficient to accurately capture the interactions between molecules and metal centers in zeolites, and indeed a multiparameter approach is necessary. Even though many of the descriptors are directly correlated, we identify the position of the s orbital and the number of valence electrons of the active site as well as the HOMO–LUMO gap of the adsorbate as most important descriptors. Furthermore, the reconstruction of the active sites upon adsorption plays a crucial role, and when it is explicitly included in the analysis, correlations improve significantly. In the future we expect that the fundamental methodology developed here will be adapted and transferred to selected problems in adsorption and catalysis and will assist the rational design of materials for the given application.
Co-reporter:Carlos A. Carrero;Samuel P. Burt;Fangying Huang;Juan M. Venegas;Alyssa M. Love;Philipp Mueller;Hao Zhu;Joseph T. Grant;Ricardo Mathison;Michael P. Hanraham;Aaron Rossini;Madelyn Ball;James Dumesic
Catalysis Science & Technology (2011-Present) 2017 vol. 7(Issue 17) pp:3707-3714
Publication Date(Web):2017/08/29
DOI:10.1039/C7CY01036B
A series of supported two- and three-dimensional vanadium oxide surface species on β-SiC with various V coverages are prepared via incipient wetness impregnation and characterized by a variety of ex and in situ techniques. The oxidative dehydrogenation of propane (ODHP) is also used as a probe reaction to complementarily distinguish between two- and three-dimensional VOx surface species. Herein, we show that treating pristine β-SiC with oxygen transforms the existing amorphous SiOxCy surface layer into a more SiO2-type layer, though with a negligible formation of Si–OH sites, which initially were expected to be the anchor sites for VOx species. In its place, the C–OH functional groups identified by X-ray photoelectron spectroscopy (XPS) act as anchor sites for the VOx species during the impregnation process, and are consumed as a function of V coverage. Our experimental observations all corroborate the formation of two- and three-dimensional VOx species on the surface of β-SiC.
Co-reporter:Carlos A. Carrero;Samuel P. Burt;Fangying Huang;Juan M. Venegas;Alyssa M. Love;Philipp Mueller;Hao Zhu;Joseph T. Grant;Ricardo Mathison;Michael P. Hanrahan;Aaron Rossini;Madelyn Ball;James Dumesic
Catalysis Science & Technology (2011-Present) 2017 vol. 7(Issue 18) pp:4232-4232
Publication Date(Web):2017/09/18
DOI:10.1039/C7CY90081C
Correction for ‘Supported two- and three-dimensional vanadium oxide species on the surface of β-SiC’ by Carlos A. Carrero et al., Catal. Sci. Technol., 2017, DOI: 10.1039/c7cy01036b.
Co-reporter:Philipp Müller and Ive Hermans
Industrial & Engineering Chemistry Research 2017 Volume 56(Issue 5) pp:
Publication Date(Web):January 13, 2017
DOI:10.1021/acs.iecr.6b04855
In situ and operando spectroscopic techniques are crucial for our understanding of complex heterogeneously catalyzed reactions. Under actual reaction conditions, however, many phenomena such as adsorption, (by)-product formation, and desorption of various species in different phases occur simultaneously, leading to crowded spectra that are difficult to interpret. About 15 years ago, modulation excitation spectroscopy (MES) was introduced to the heterogeneous catalysis community and has been increasingly applied since then. The periodic perturbation of a given system, in combination with phase-sensitive detection (PSD) analysis, significantly reduces noise, distinguishes between active and spectator species, and enables extraction of kinetic information. In this review article, we discuss the origin and theory of MES, summarize different application examples (with an emphasis on heterogeneous catalysis), and suggest future developments of the technique.
Co-reporter:Philipp Müller, Patrick Wolf, and Ive Hermans
ACS Catalysis 2016 Volume 6(Issue 5) pp:2760
Publication Date(Web):March 16, 2016
DOI:10.1021/acscatal.5b02493
Heterogeneously catalyzed liquid-phase reactions are highly complex chemical systems. As the local molecular composition close to the active site is often unknown, sophisticated spectroscopic tools are needed to gain insights on a molecular level. One solution to these challenges is the use of modulation excitation spectroscopy with attenuated total reflection infrared spectroscopy. We use this highly sensitive and selective technique to study the Lewis acid-catalyzed cyclization of citronellal over mesoporous Sn-SBA-15 and microporous Sn-Beta. We find that the reaction mechanism is generally similar for the two materials. However, the confined space at the active site within the zeolite stabilizes the coordination of citronellal to the SnIV site and prevents byproduct formation, as well as the reverse reaction due to size-exclusion of the product isopulegol. The use of the Lewis base acetonitrile as solvent reduces the catalytic performance with Sn-SBA-15 drastically, while Sn-Beta remains highly active. Infrared spectra reveal a simultaneous coordination of citronellal and acetonitrile to the tin site in Sn-Beta, whereas in Sn-SBA-15, the more-accessible SnIV site leads to much stronger and hence detrimental competitive adsorption. The results obtained in this study indicate that the substrate–catalyst–solvent combination needs to be optimized in order to maximize the performance of solid–liquid reactions.Keywords: confinement; in situ infrared spectroscopy; modulation excitation; Sn-Beta; solvent effect; stannosilicate
Co-reporter:Alyssa M. Love, Carlos A. Carrero, Alessandro Chieregato, Joseph T. Grant, Sabrina Conrad, René Verel, and Ive Hermans
Chemistry of Materials 2016 Volume 28(Issue 15) pp:5495
Publication Date(Web):June 13, 2016
DOI:10.1021/acs.chemmater.6b02118
We investigate the chemical reactions involved during the synthesis of supported vanadium oxide catalysts using chemical grafting of vanadium oxytriisopropoxide (VO(OiPr)3) to thermally pretreated silica under solvent-free conditions. VO(OiPr)3 is found to react with both site-isolated silanol (Si−OH) groups and strained siloxane (≡Si−O−Si≡) bridges at the silica surface. Solid-state 51V and 13C MAS NMR confirms the formation of two slightly different vanadium species associated with the two anchoring mechanisms. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), in situ Raman spectroscopy, and thermogravimetric analysis-differential scanning calorimetry-mass spectrometry (TGA-DSC-MS) were used to study the subsequent calcination, revealing the formation of a transient V—OH intermediate upon the release of propene, followed by the formation of isolated VO4 surface species upon elimination of water. X-ray absorption spectroscopy (XAS) and 51V MAS NMR of the calcined material confirm the conversion of the two original vanadium sites to a species with a single isotropic shift, confirming the formation of isolated, tetrahedral VO4 sites.
Co-reporter:Zhuoran Xu, Joseph P. Chada, Dongting Zhao, Carlos A. Carrero, Yong Tae Kim, Devon C. Rosenfeld, Jessica L. Rogers, Steven J. Rozeveld, Ive Hermans, and George W. Huber
ACS Catalysis 2016 Volume 6(Issue 6) pp:3815
Publication Date(Web):May 4, 2016
DOI:10.1021/acscatal.6b00655
Linear octenes were produced in high (70–85%) selectivity from oligomerization of liquid 1-butene using carbon-supported cobalt oxide catalysts in a continuous flow reactor. The liquid products were characterized by two-dimensional gas chromatography–mass spectrometry. Above 95% of the oligomers were C8 olefins, with the other products primarily being branched C12 olefins. The linear octene products at a conversion of 9.77% decreased in selectivity according to 3-octene > trans-2-octene > cis-2-octene > 4-octene. Methyl-heptenes including trans/cis-5-methyl-2-heptene > trans/cis-5-methyl-3-heptene > trans-3-methyl-2-heptene (at the lowest conversion) were the other major products summing to 15.6%. The selectivity of linear octenes decreased from 84 to 78% as the conversion increased from 10% to 29%. The product distribution suggests the reaction pathway involves a head-to-head coupling of two 1-butene molecules to form internal linear octenes. Head-to-tail coupling of two 1-butene molecules or a coupling between 1-butene and 2-butene forms the observed methyl-heptenes. The rate of head-to-head coupling is higher than the rate of head-to-tail or the rate of 1-butene to 2-butene coupling as indicated by the higher selectivity of linear octenes. The activated catalyst contained both Co3O4 and CoO as confirmed by X-ray diffraction (XRD), in situ Raman spectroscopy, and X-ray absorption spectroscopy. The cobalt oxide particle size was estimated to be between 5 and 10 nm by high-resolution transmission electron microscopy and XRD. The Co3O4/CoO ratio decreased with increasing pretreatment temperature. Metallic cobalt, which has a low catalytic activity, formed at 550 °C.Keywords: heterogeneous catalysis; linear octene; oligomerization; pretreatment temperature; selectivity
Co-reporter:Patrick Wolf, Maxence Valla, Francisco Núñez-Zarur, Aleix Comas-Vives, Aaron J. Rossini, Connor Firth, Hana Kallas, Anne Lesage, Lyndon Emsley, Christophe Copéret, and Ive Hermans
ACS Catalysis 2016 Volume 6(Issue 7) pp:4047
Publication Date(Web):May 11, 2016
DOI:10.1021/acscatal.6b00114
Sn-β zeolites prepared using different recipes feature very different catalytic activities for aqueous phase glucose isomerization, suggesting the presence of different active sites. A systematic study of the morphology and atomic-level structure of the materials using DNP NMR spectroscopy in combination with first-principles calculations allows for the discrimination between potential sites and leads to a proposal of specific structural features that are important for high activity. The results indicate that the materials showing the highest activity possess a highly hydrophobic, defect-free zeolite framework. Those materials show so-called closed and associated partially hydrolyzed Sn(IV) sites in the T6 and T5/T7 lattice positions. On the other hand, postsynthetically synthesized Sn-β samples prepared in two steps via dealumination and subsequent solid-state ion exchange from Al-β show significantly lower activity, which is associated with a hydrophilic framework and/or a lower accessibility and different lattice position of the Sn sites in the zeolite crystal. Further, we provide a method to distinguish between different Sn sites on the basis of NMR cartography using chemical shift and chemical shift anisotropy as readily measurable parameters. This cartography allows identifying not only the nature of the active sites (closed, defect-open, and hydrolyzed-open) but also their position within the BEA framework.Keywords: 119Sn solid-state NMR; ab initio calculations; DNP SENS; glucose isomerization; Sn-β zeolites; stannosilicates
Co-reporter:Philipp Müller, Samuel P. Burt, Alyssa M. Love, William P. McDermott, Patrick Wolf, and Ive Hermans
ACS Catalysis 2016 Volume 6(Issue 10) pp:6823
Publication Date(Web):September 5, 2016
DOI:10.1021/acscatal.6b01642
In recent years, the on-purpose production of 1,3-butadiene (BD) from renewable resources such as ethanol has received increased attention. In that context, Lewis acid catalysts play an important role, especially in the two-step process, i.e. when a mixture of acetaldehyde and ethanol is used as substrate. As the reaction mechanism consists of many intermediates and occurs over different catalytic functionalities, it is notoriously difficult to gain molecular-level insights into the mechanism. Here, we present a study on Lewis acidic Ta-BEA and propose a plausible reaction mechanism. We developed an operando DRIFTS-MS setup that allows for precise control and analysis of changes in the gas-phase composition as well as surface species. Using this tool, we found a surface intermediate with a vibrational frequency at 1690 cm–1 that is only formed in the presence of both ethanol and crotonaldehyde and that is likely involved in the production of BD. Our data further suggests that a subtle control of the ratio of ethanol to acetaldehyde is crucial to keep a high ethoxy coverage and to desorb the intermediate crotyl alcohol in order to achieve high BD productivity. To the best of our knowledge, this is the first dynamic operando spectroscopic study on this re-emerging reaction.Keywords: butadiene; C−C coupling; DRIFTS-MS; ethanol; Lewis acids; operando spectroscopy; zeolites
Co-reporter:J. T. Grant;C. A. Carrero;F. Goeltl;J. Venegas;P. Mueller;S. P. Burt;S. E. Specht;W. P. McDermott;A. Chieregato;I. Hermans
Science 2016 Vol 354( Iss 6319) pp:
Publication Date(Web):23 Dec 2016
DOI:10.1126/science.aaf7885
Boron nitride catalysis
Propene is one of the highest-volume organic chemicals produced. Propene has mainly been made from naphtha, but changes in the global supply chain are creating shortages. Direct conversion from propane, a component of natural gas, via reaction with oxygen is an attractive alternative, but existing approaches produce a large fraction of unwanted CO and CO2. Grant et al. report that boron nitride, normally an unreactive material, has high selectivity to catalyze the production of propene (77%) and ethene (13%).
Science, this issue p. 1570
Co-reporter:Joseph T. Grant;Alyssa M. Love;Carlos A. Carrero;Fangying Huang
Topics in Catalysis 2016 Volume 59( Issue 17-18) pp:1545-1553
Publication Date(Web):2016 October
DOI:10.1007/s11244-016-0671-2
The oxidative dehydrogenation of propane (ODHP) is an attractive reaction for the on-purpose production of propylene. Unfortunately, rapid consecutive over-oxidation of the desired olefin limits the selectivity and hampers the industrial feasibility. Supported metal oxides, and in particular dispersed vanadium-containing materials, have shown promising results. Yet one has to improve both the selectivity and activity (space–time–yield) to make this reaction attractive. In this contribution we build upon our previous work that allowed us to increase the dispersion of group V metal oxides on silica using a sodium promoter. Using Raman spectroscopy and 51V MAS NMR, we postulate that the minor decrease in our observed turnover frequency (TOF) for ODHP using sodium-promoted materials may be due to Na+ ions weakly interacting with the V=O site, responsible for the initial H-atom abstraction. While our observed TOF is well within the range of literature reported TOF for these materials, such a large deviation in reported TOF (varying almost three orders of magnitude) may be due to various impurities used in the silica of these previously reported studies. Subsequently, we prepared a ternary metal oxide catalyst based on vanadium and tantalum that shows superior selectivity and productivity. Indeed, productivity of a combined V- and Ta-oxide catalyst supported on silica doubles the productivity of catalysts with low loadings of vanadium oxide supported on silica. The reasons for the significant improvement are currently under investigation.
Co-reporter:Joseph T. Grant, Carlos A. Carrero, Alyssa M. Love, René Verel, and Ive Hermans
ACS Catalysis 2015 Volume 5(Issue 10) pp:5787
Publication Date(Web):August 24, 2015
DOI:10.1021/acscatal.5b01679
The catalytic performance of supported metal oxides is often controlled by their two- or three-dimensional dispersion. Silica, one of the popular inert supports, triggers the undesired formation of three-dimensional nanoparticles at significantly lower loadings than other conventional supports like Al2O3, TiO2, Nb2O5, or ZrO2. This observation has been ascribed to the lower reactivity of surface SiOH groups toward the precursor, compared to other metal hydroxyl groups on different supports. In this contribution, we show that by promoting amorphous silica with low amounts of sodium, the surface density of two-dimensional metal oxide species can be significantly enhanced to the same level as all other oxide supports previously reported in the literature. This effect is demonstrated for the case of supported vanadia using a variety of spectroscopic techniques (i.e., Raman, diffuse reflectance UV–vis, and 51V-MAS NMR), as well as a catalytic activity study for the oxidative dehydrogenation of propane (ODHP), a structure-sensitive probe reaction. The propane consumption rate was found to increase linearly with the vanadium surface density while the propylene selectivity was not affected until a monolayer coverage of ca. 9 vanadia per nm2 was surpassed. The method is also applicable to other group V metals (i.e., Nb- and Ta-oxide), opening new perspectives for supported metal oxides.Keywords: metal oxide monolayer; metal oxide nanoparticles; oxidative propane dehydrogenation; supported metal oxides; vanadium oxide
Co-reporter:Sabrina Conrad;Dr. René Verel;Dr. Ceri Hammond;Patrick Wolf;Dr. Florian Göltl;Dr. Ive Hermans
ChemCatChem 2015 Volume 7( Issue 20) pp:3270-3278
Publication Date(Web):
DOI:10.1002/cctc.201500630
Abstract
SnIV-substituted zeolites show remarkable activity for important Lewis acid catalyzed reactions. In such complex catalytic systems it is, however, difficult to untangle the influence of all parameters contributing to the overall performance, and hence to rationally improve the catalyst. In this work, we studied silica-grafted SnIV sites to reduce this complexity by eliminating the potential influence of pore confinement. The surface-anchored SnIV sites were modified by calcination and silylation to increase Lewis acidity and hydrophobicity. Various techniques were used to characterize the materials, including the adsorption of cyclohexanone by using FTIR spectroscopy. We relate our spectroscopic results with catalytic tests and compare our model catalysts with benchmark Snβ zeolite. This suggested that besides active-site structure, also hydrophobicity and confinement effects influence the activity. Our work demonstrates the utility of model systems to separate the different contributions to catalytic activity.
Co-reporter:Sabrina Conrad;Dr. René Verel;Dr. Ceri Hammond;Patrick Wolf;Dr. Florian Göltl;Dr. Ive Hermans
ChemCatChem 2015 Volume 7( Issue 20) pp:
Publication Date(Web):
DOI:10.1002/cctc.201501018
Co-reporter:Sabrina Conrad;Dr. René Verel;Dr. Ceri Hammond;Patrick Wolf;Dr. Florian Göltl;Dr. Ive Hermans
ChemCatChem 2015 Volume 7( Issue 20) pp:
Publication Date(Web):
DOI:10.1002/cctc.201500943
Abstract
The front cover artwork for Issue 20/2015 is provided by the Hermans research group at the University of Wisconsin-Madison (formerly located at the Swiss Federal Institute of Technology, Zurich). The image shows silica-supported Lewis acidic SnIV sites that are tuned to be catalytically active in the Meerwein–Ponndorf–Verley reduction of cyclohexanone with 2-butanol. See the Full Paper itself at http://dx.doi.org/10.1002/cctc.201500630.
Co-reporter:Christof Aellig, Florian Jenny, David Scholz, Patrick Wolf, Isabella Giovinazzo, Fabian Kollhoff and Ive Hermans
Catalysis Science & Technology 2014 vol. 4(Issue 8) pp:2326-2331
Publication Date(Web):14 Apr 2014
DOI:10.1039/C4CY00213J
The oxygen-free lactonization of 1,4-butanediol to γ-butyrolactone coupled with a sequential reductive upgrading of furfural derivatives following a transfer hydrogenation/hydrogenolysis mechanism was studied over AlOx-supported copper catalysts. The Cu–Al hydrotalcite-like catalyst-precursor was first reduced with H2, forming dispersed Cu nanoparticles. The catalyst was characterized and tested for the dehydrogenation of various primary and secondary alcohols, optimizing the activation procedure and reaction conditions. Subsequently, the combined transfer hydrogenation/hydrogenolysis to furfural derivatives was investigated. All reactions were performed under continuous flow conditions to increase the space-time yield and the selectivity towards the desired products, as well as to study the catalyst stability.
Co-reporter:Ive Hermans;Joaquim Henrique Teles;Richard Dehn
Topics in Catalysis 2014 Volume 57( Issue 14-16) pp:1256-1264
Publication Date(Web):2014 September
DOI:10.1007/s11244-014-0291-7
In this contribution we use computational tools to investigate the reaction of alcohol substrates with reactive nitrogen oxide species such as N2O3 and N2O4, leading to the formation of alkyl nitrites. These nitrites are interesting intermediates which can be processed to various valuable chemicals such as ketones/aldehydes and dimethyl oxalate while regenerating NOx. As such, NOx is used as an oxidation mediator, converting alcohol substrates to more reactive nitrites which can be selectively converted to more desired compounds, closing a catalytic cycle in NOx species.
Co-reporter:Patrick Wolf;Maxence Valla;Dr. Aaron J. Rossini;Dr. Aleix Comas-Vives;Dr. Francisco Núñez-Zarur;Dr. Bernard Malaman;Dr. Anne Lesage;Dr. Lyndon Emsley;Dr. Christophe Copéret;Dr. Ive Hermans
Angewandte Chemie International Edition 2014 Volume 53( Issue 38) pp:10179-10183
Publication Date(Web):
DOI:10.1002/anie.201403905
Abstract
Dynamic nuclear polarization surface enhanced NMR (DNP-SENS), Mössbauer spectroscopy, and computational chemistry were combined to obtain structural information on the active-site speciation in Sn-β zeolite. This approach unambiguously shows the presence of framework SnIV-active sites in an octahedral environment, which probably correspond to so-called open and closed sites, respectively (namely, tin bound to three or four siloxy groups of the zeolite framework).
Co-reporter:Christof Aellig, Florian Jenny, David Scholz, Patrick Wolf, Isabella Giovinazzo, Fabian Kollhoff and Ive Hermans
Catalysis Science & Technology (2011-Present) 2014 - vol. 4(Issue 8) pp:NaN2331-2331
Publication Date(Web):2014/04/14
DOI:10.1039/C4CY00213J
The oxygen-free lactonization of 1,4-butanediol to γ-butyrolactone coupled with a sequential reductive upgrading of furfural derivatives following a transfer hydrogenation/hydrogenolysis mechanism was studied over AlOx-supported copper catalysts. The Cu–Al hydrotalcite-like catalyst-precursor was first reduced with H2, forming dispersed Cu nanoparticles. The catalyst was characterized and tested for the dehydrogenation of various primary and secondary alcohols, optimizing the activation procedure and reaction conditions. Subsequently, the combined transfer hydrogenation/hydrogenolysis to furfural derivatives was investigated. All reactions were performed under continuous flow conditions to increase the space-time yield and the selectivity towards the desired products, as well as to study the catalyst stability.
