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We propose a novel high-throughput workflow, combining DFT-derived atomic scale interaction parameters with experimental data to identify key performance-related descriptors in a CO2 to methanol reaction, for In-based catalysts. Utilizing advanced machine learning algorithms suitable for small datasets, secondary descriptors with high predictive power for catalytic activity were constructed. These descriptors, which highlight the crucial role of hydroxyl sites, can be applied to designing new materials and to bringing them to the test with high-throughput screening, paving the path for accelerated catalyst design.

The direct hydrogenation of CO2 to methanol is an attractive approach to employ the greenhouse gas as a chemical feedstock. However, the commercial copper catalyst, used for methanol synthesis from CO-rich syngas, suffers from deactivation at elevated CO2 partial pressure. An emerging alternative is represented by In2O3 as it withstands the hydrothermal conditions induced by the reverse water-gas shift reaction. The active sites for the adsorption of CO2 and the subsequent conversion into methanol were shown to be oxygen vacancies on the surface of In2O3. In this study, N2O was utilized as a probe molecule to quantify the number of vacancies on indium oxide catalysts. The number of inserted oxygen atoms could be correlated to the respective CO2 hydrogenation activity. Furthermore, the atomic efficiency of indium was enhanced by applying atomic layer deposition of indium oxide on ZrO2.

Ni supported on alumina is extensively employed as a catalyst for the reverse water gas shift reaction. However, the formation of inactive Ni aluminates and the high selectivity to methane affects the performance of these catalysts, especially at low reaction temperatures. In this study, Cu is employed as an effective enhancer of the catalytic performance, promoting the reducibility of Ni, and suppressing methane production through the formation of stable CuNi nanoalloys. The synergy between both metals suppresses consecutive hydrogenation, reaching conversions close to equilibrium and 100% selectivity to carbon monoxide. At 500 °C, the CO yield of the Cu25Ni75/Al2O3 catalyst was twice that of Ni/Al2O3, with only half the hydrogen consumption. The formation of CuNi nanoalloys was confirmed by HAADF STEM–EDS, without segregation in monometallic phases even after 30 h time on stream. Similarly, Cu50Ni50/Al2O3 remained alloyed after the reaction. However, the catalytic activity decreased due to sintering, in agreement with a higher Cu content. This effect was significantly more pronounced for Cu75Ni25/Al2O3 and Cu/Al2O3, with formation of large particles and consequent loss of active surface area.

Atomic layer deposition (ALD) of POx on V2O5 powder was applied as a tool to tailor active and selective sites of a bulk catalyst. ALD leads to homogeneous P deposition on the V2O5 surface with linear increase of P content with each ALD cycle. The catalyst performance was evaluated and correlated to structural motifs identified by detailed characterization methods. The catalytic conversion of butane to maleic anhydride (MAN) was chosen as proof-of-concept reaction. The selectivity towards MAN increases with ALD cycle number from 1–3 ALD cycles and remains constant at higher ALD cycles. Restructuring of the catalyst surface is induced by steam during reaction conditions at elevated temperatures. Excessive P is migrating away from the catalyst surface to form various VOPO4 polymorphs revealing partially but homogeneously covered V2O5 by P. The formed VOPO4 species barely contribute to the yield to MAN. Solid-state 31P-NMR was used to identify fingerprints relevant for selectivity and activity. This work shows that synthesizing model catalysts by atomic layer deposition combined with detailed analytics can reveal property-performance relationships.

As-prepared materials tested for a catalytic reaction are usually only precatalysts that become active and/or selective under specific conditions. During this initial formation phase, catalysts can undergo a change in their structure, morphology, chemical state, or even composition. This dynamic behavior has a vital impact on reactivity, and we identified that this initial formation phase is also critical for Rh in the catalytic conversion of synthesis gas to oxygenates and ethanol in particular. The syngas-to-ethanol reaction (StE) is a promising alternative route to ethanol from fossil and nonfossil carbon resources. Despite heavy research efforts, rates and selectivities still need to be improved for industrial operations. For this reason, structure–function relationships at industrially relevant reaction conditions must be clarified. Although some in situ and operando studies have been reported, a pressure gap still exists between experimental and process-relevant high-pressure conditions. To overcome this pressure gap and investigate the dynamic behavior of Rh-based catalysts under reaction conditions, we applied a generic method for formation phase studies at high partial pressures of synthesis gas where standard operando methods are inapplicable. Combining integral and local characterization methods before and after a long-term catalytic test of a RhFeOx/SiO2 catalyst (>140 h on stream) allowed us to ascribe a drastic decrease in ethanol formation to a structural change from an unalloyed RhFeOx to an alloyed RhFe/FeOx nanostructure. Our investigation provides an explanation for the great variation of reported catalytic results of RhFe catalysts and their nanostructures in synthesis gas conversion. The structure–function relationship we identified finally provides the opportunity for improved catalyst design strategies: stabilizing the Rh–FeOx interface by preventing RhFe nanoalloy formation. As one example, we report a RhFeOx catalyst on a high surface area Mn2O3 support which decreases the Fe mobility and reducibility through the formation of a (Fe,Mn)Ox mixed surface oxide. Stabilizing the Rh–FeOx interface finally led to stable ethanol selectivity, and the formation of RhFe nanoalloy structures was not observed.

Atomic layer deposition is a rising technique for catalyst synthesis and modification. Typically, the focus of ALD in catalysis is on supported metal nanoparticles. Here, the authors give mechanistic insights into the ALD of oxides on redox active catalysts by a combination of in situ analytics, such as XPS, DRIFTS and gravimetric measurements. Phosphorus oxide and aluminum oxide were deposited on divanadium pentoxide powder in a fixed bed reactor. In contrast to the generally accepted concepts, the first half cycle does not proceed over surface hydroxyl groups but involves redox chemistry between the precursor and the vanadium atoms, as shown by 31P-SSNMR and XPS. For POx deposition, a temperature step from 150 °C in the first half cycle to 450 °C in the second half cycle is needed to obtain linear mass gain per cycle as the remaining ligands are combusted and reduced vanadium atoms are reoxidized. Homogeneous deposition was confirmed by STEM-EDX and XRD showing no additional phases, despite performing up to 10 ALD cycles. Even the well-known process of alumina ALD confirms the involvement of reduction–oxidation reactions between the ALD precursor and the substrate V2O5. However, redox chemistry can be suppressed for alumina ALD at low temperatures of 50 °C. Therefore, this study shows that ALD on oxidation catalysts is complex and thus the developed ALD processes are unusual compared to ALD on typical supports, such as SiO2 or Al2O3.

A low amount of AlOx was successfully deposited on an unordered, mesoporous SiO2 powder using 1–3 ALD (Atomic Layer Deposition) cycles of trimethylaluminium and water. The process was realized in a self-built ALD setup featuring a microbalanceand a fixed particle bed. The reactor temperature was varied between 75, 120, and 200 °C. The self-limiting nature of the deposition was verified by in situ gravimetric monitoring for all temperatures. The coated material was further analyzed by nitrogen sorption, inductively coupled plasma-optical emission spectroscopy, powder X-ray diffraction, high-resolution transmission electron microscopy, attenuated total reflection Fourier transformed infrared spectroscopy, and elemental analysis. The obtained mass gains correspond to average growth between 0.81–1.10 Å/cycle depending on substrate temperature. In addition, the different mass gains during the half-cycles in combination with the analyzed aluminum content after one, two, and three cycles indicate a change in the preferred surface reaction of the trimethylaluminium molecule from a predominately two-ligand exchange with hydroxyl groups to more single-ligand exchange with increasing cycle number. Nitrogen sorption isotherms demonstrate (1) homogeneously coated mesopores, (2) a decrease in surface area, and (3) a reduction of the pore size. The experiment is successfully repeated in a scale-up using a ten times higher substrate batch size.

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Review of Scientific Instruments 88, 074102 (2017) and may be found at https://doi.org/10.1063/1.4992023., A modular setup for Atomic Layer Deposition (ALD) on high-surface powder substrates in fixed bed reactors with a gravimetric in situ monitoring was developed. The design and operation are described in detail. An integrated magnetically suspended balance records mass changes during ALD. The highly versatile setup consists of three modular main units: a dosing unit, a reactor unit, and a downstream unit. The reactor unit includes the balance, a large fixed bed reactor, and a quartz crystal microbalance. The dosing unit is equipped with a complex manifold to deliver gases and gaseous reagents including three different ALD precursors, five oxidizing or reducing agents, and two purge gas lines. The system employs reactor temperatures and pressures in the range of 25-600 °C and 10−3 to 1 bar, respectively. Typically, powder batches between 100 mg and 50 g can be coated. The capabilities of the setup are demonstrated by coating mesoporous SiO2 powder with a thin AlOx (submono) layer using three cycles with trimethylaluminium and H2O. The self-limiting nature of the deposition has been verified with the in situ gravimetric monitoring and full saturation curves are presented. The process parameters were used for a scale-up in a large fixed bed reactor. The samples were analyzed with established analytics such as X-ray diffraction, N2 adsorption, transmission electron microscopy, and inductively coupled plasma optical emission spectrometry.