Degree Of Rate Control Analysis Research Articles

CO2 Hydrogenation on Ru Single-Atom Catalyst Encapsulated in Silicalite: a DFT and Microkinetic Modeling Study.

The critical levels of CO2 emissions reached in the past decade have encouraged researchers into finding techniques to reduce the amount of anthropogenic CO2 expelled to the atmosphere. One possibility is to capture the produced CO2 from the source of emission or even from air (i.e., direct air capture) by porous materials (e.g., zeolites and MOFs). Among the different usages of captured CO2, its conversion into light fuels such as methane, methanol, and formic acid is essential for ensuring the long-awaited circular economy. In the last years, single-atom catalysts encapsulated in zeolites have been considered to this purpose since they exhibit a high selectivity and activity with the minimum expression of catalytic species. In this study, a detailed mechanism composed by 47 elementary reactions, 42 of them in both forward and reverse directions and 5 of them that correspond to the desorption of gas products just forwardly studied), has been proposed for catalytic CO2 hydrogenation over Ru SAC encapsulated in silicate (Ru1@S-1). Periodic density functional theory (DFT) calculations along with microkinetic modeling simulations at different temperatures and pressures were performed to evaluate the evolution of species over time. The analysis of the results shows that carbon monoxide is the main gas produced, followed by formic acid and formaldehyde. The rate analysis shows that CO(g) is formed mainly through direct dissociation of CO2 (i.e., redox mechanism), whereas COOH formation is assisted by OH. Moreover, the Campbell's degree of rate control analysis suggests that the determining steps for the formation of CO(g) and CH2O(g) gas species are their own desorption processes. The results obtained are in line with recent experimental and theoretical results showing that Ru1 SACs are highly selective to CO(g), whereas few atom clusters as Ru4 increase selectivity toward methane formation.

Dry Reforming of Methane on Ni/LaZrO2 Catalyst under External Electric Fields: A Combined First-Principles and Microkinetic Modeling Study.

Dry reforming of methane (DRM) reaction has great potential in reducing the greenhouse effect and solving energy problems. Herein, the DRM reaction mechanism and activity on Ni16/LaZrO2 catalyst under electric fields were comprehensively investigated by combining density functional theory calculations with microkinetic modeling. The results showed that La doping increases the interaction between Ni and ZrO2 by Ni cluster transfer of more electrons. The adsorption strength of species followed the order Ni16/ZrO2 > Ni16/LaZrO2, which is consistent with the results for the d-band center but opposite to the metal-support interaction. The best DRM reaction path on Ni16/LaZrO2 was the CH2-O pathway, which is different from the CH-O pathway on Ni(111) and Ni16/ZrO2. Both positive and negative electric fields of strong and weak metal-support interactions reduced the energy barrier of DRM reaction. Importantly, our results showed that the more dispersed and smaller Ni12/LaZrO2 model by considering the dispersing effect induced by La doping, which displayed very different results from that of Ni16/LaZrO2: reduced the energy barrier for methane decomposition, thereby promoting DRM reaction activity. Microkinetic results showed that the carbon deposition behavior of DRM becomes weaker on Ni16/LaZrO2 due to the suppression of methane decomposition in the presence of La doping compared to Ni16/ZrO2, but the opposite result is obtained on Ni12/LaZrO2. The order of DRM reactivity was Ni16/LaZrO2 < Ni16/ZrO2 < Ni12/LaZrO2, which is consistent with the experiment observations. The conversion of methane and CO2 was higher in positive electric fields than in negative electric fields at low temperatures, but the results were opposite at high temperature. Negative electric fields can improve the carbon deposition resistance of Ni-based catalysts compared to positive electric fields. The degree of rate control analysis showed that CHx* oxidation also plays an important role in the DRM reaction. We envision that this study could provide a deeper understanding for guiding the widespread application of electric field catalysis.

First-principles-based microkinetic modeling of methanol steam reforming over Cu(111) and Cu(211): structure sensitive activity and selectivity.

The development of hydrogen energy is widely recognized as a key approach to addressing the energy and carbon emission challenges. Methanol steam reforming is a promising hydrogen production scheme that can provide high-purity hydrogen. In this work, we studied the primary reaction mechanisms of methanol steam reforming over the Cu(111) and Cu(211) surfaces using density functional theory (DFT) calculations and microkinetic simulations. A detailed kinetic perspective on the reaction mechanism, which is often overlooked in previous research that relies solely on DFT calculations, is provided in the current work. Our findings reveal that under typical experimental conditions, the dominant mechanism on the Cu(111) surface is the methyl formate mechanism, while the H2COO dehydrogenation mechanism is dominant on Cu(211). The activity over the Cu(111) surface was slightly higher than that over Cu(211). Based on the degree of rate control analysis results, a reaction rate equation was derived to quantitatively explain the trend of activity under different operating conditions. It was also found that CO2 selectivity was significantly higher over Cu(211) than over the Cu(111) surface. Furthermore, based on the Wulff construction scheme, copper nanoparticle models with different sizes were constructed, and a detailed structure sensitivity study was executed. This comprehensive investigation sheds light on the mechanisms of methanol steam reforming reactions over the Cu(111) and Cu(211) surfaces, providing essential insights for the design of high-performance catalysts for hydrogen production.

Mechanistic Insights into Nonoxidative Ethanol Dehydrogenation on NiCu Single-Atom Alloys

Ethanol dehydrogenation presents a promising pathway toward the production of acetaldehyde, a valuable building block in chemicals production. Under nonoxidative conditions, the reaction is facilitated by supported Cu nanoparticles, which afford reasonable activity and high selectivity. The stability issues associated with Cu nanoparticle sintering can be addressed by the addition of small amounts of Ni, which further boost reactivity while retaining selectivity. Despite the promise of NiCu single-atom alloys for nonoxidative ethanol dehydrogenation, little is known about the role of each component and the pathway of this mechanistically complex process. Herein, kinetic investigations from reactor tests identify C–H bond scission as the rate-limiting step, while 1-hydroxyethyl is detected as the intermediate via IR spectroscopy. Temperature-programmed desorption studies are employed to examine the effect of Ni coverage and to demonstrate that Ni atoms activate ethanol selectively at lower temperatures, resulting in higher acetaldehyde yield than pure Cu. Temperature-programmed desorption experiments also reveal the spillover of intermediates from the Ni atom to neighboring Cu sites as a relevant step in the reaction pathway. Density functional theory calculations are used to investigate the reaction energetics and to confirm that C–H bond scission is the initial reaction step, while a clear effect of H2 partial pressure on the reaction pathway is realized. Further, counter to the expected behavior that all reaction steps take place on the Ni atoms, our degree of rate control analysis reveals that a mechanism involving spillover of the 1-hydroxyethyl intermediate from the Ni atom to the Cu surface, where it will dehydrogenate further, is more likely. Our combined kinetic, spectroscopic, and theoretical approach sheds light on this complex reaction mechanism and represents a promising method for the understanding and designing of highly active, selective, and stable single-atom alloys for other multistep catalytic processes.

Comparison of Heterogeneous Hydroformylation of Ethylene and Propylene over RhCo3/MCM-41 Catalysts

The reaction mechanisms of heterogeneous hydroformylation of ethylene and propylene were compared at 413–453 K using RhCo3/MCM-41 as catalysts. The reaction rates of propylene for both hydroformylation and the undesired side reaction of hydrogenation were found to be about one order of magnitude lower than those for ethylene in flow reactor studies. The difference in the kinetic behavior between ethylene and propylene was investigated by measuring the reaction orders and apparent activation energies, and these macrokinetic observables were analyzed using the degree of rate control (DRC) method. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) experiments were performed to characterize the surface intermediates formed during the reactions. When the reactant was changed from ethylene to propylene, the IR peak corresponding to adsorbed CO exhibited a significant increase, while the IR peaks of the alkyl group decreased in magnitude. Combined with the DRIFTS results, DRC analysis indicates that the first step of olefin hydroformylation, the formation of an alkyl group on the catalyst surface, plays a key role in the difference between ethylene and propylene. This step is kinetically nonrelevant when ethylene is the reactant, but it is one of the rate-controlling steps for propylene. The low concentration of the adsorbed propyl group, which is a common intermediate shared by both hydroformylation and hydrogenation of propylene, decreases the rates of both reaction pathways as compared to ethylene.

First-Principles Microkinetic Model for Low-Temperature NH3-Assisted Selective Catalytic Reduction of NO over Cu-CHA

A first-principles microkinetic model is developed to investigate the low-temperature ammonia-assisted selective catalytic reduction (NH3-SCR) of NO over Cu-chabazite (Cu-CHA). The reaction proceeds over NH3-solvated Cu sites by the formation of H2NNO and HONO, which decompose to N2 and H2O over Brønsted acid sites. Nonselective N2O formation is considered by H2NNO decomposition over the Cu sites. The adsorption of NH3 at oxidized Cu sites is found to inhibit the reaction at low temperatures by hindering NO adsorption. For the reactions, we find positive reaction orders with respect to NO and O2, whereas the reaction order with respect to NH3 is negative. The reaction orders and the obtained apparent activation energy are in good agreement with experimental data. A degree of rate control analysis shows that NH3-SCR over a pair of Cu(NH3)2+ is mainly controlled by NO adsorption below 200 °C, whereas the formation of HONO and H2NNO becomes controlling at higher temperatures. The successful formulation of a first-principles microkinetic model for NH3-SCR rationalizes previous phenomenological models and links the kinetic behavior with materials properties, which results in unprecedented insights into the function of Cu-CHA catalysts for NH3-SCR.

Quantifying the Impact of Parametric Uncertainty on Automatic Mechanism Generation for CO2 Hydrogenation on Ni(111).

Automatic mechanism generation is used to determine mechanisms for the CO2 hydrogenation on Ni(111) in a two-stage process while considering the correlated uncertainty in DFT-based energetic parameters systematically. In a coarse stage, all the possible chemistry is explored with gas-phase products down to the ppb level, while a refined stage discovers the core methanation submechanism. Five thousand unique mechanisms were generated, which contain minor perturbations in all parameters. Global uncertainty assessment, global sensitivity analysis, and degree of rate control analysis are performed to study the effect of this parametric uncertainty on the microkinetic model predictions. Comparison of the model predictions with experimental data on a Ni/SiO2 catalyst find a feasible set of microkinetic mechanisms within the correlated uncertainty space that are in quantitative agreement with the measured data, without relying on explicit parameter optimization. Global uncertainty and sensitivity analyses provide tools to determine the pathways and key factors that control the methanation activity within the parameter space. Together, these methods reveal that the degree of rate control approach can be misleading if parametric uncertainty is not considered. The procedure of considering uncertainties in the automated mechanism generation is not unique to CO2 methanation and can be easily extended to other challenging heterogeneously catalyzed reactions.

A DFT-based microkinetic study on methanol synthesis from CO2 hydrogenation over the In2O3 catalyst.

In this work, we performed density functional theory (DFT)-based microkinetic simulations to elucidate the reaction mechanism of methanol synthesis on two of the most stable facets of the cubic In2O3 (c-In2O3) catalyst, namely the (111) and (110) surfaces. Our DFT calculations show that for both surfaces, it is difficult for the H atom adsorbed at the remaining surface O atom around the O vacancy (Ov) active site to migrate to an O adsorbed at the Ov due to the very high energy barrier involved. In addition, we also find that the C-O bond in the bt-CO2* chemisorption structure can directly break to form CO with a lower energy barrier than that in its hydrogenation to the COOH* intermediate in the COOH route. However, our microkinetic simulations suggest that for both surfaces, CO2 deoxygenation to form CO in both pathways, namely the COOH and CO-O routes, are kinetically slower than methanol formation under typical steady state conditions assuming a CO2 conversion of 10% and a CO selectivity of 1%. Although these results agree with previous experimental observations at relatively low reaction temperature, where methanol formation dominates, they cannot explain the predominant formation of CO at relatively high reaction temperature. We tentatively attribute this to the simplicity of our microkinetic model as well as possible structural changes of the catalyst at relatively high reaction temperature. Furthermore, although the rate-determining step (RDS) from the degree of rate control (DRC) analysis is usually consistent with that judged from the DFT calculated energy barriers, for CO2 hydrogenation to methanol over the (111) surface, our DRC analysis suggests homolytic H2 dissociation to be the rate-controlling step, which is not apparent from the DFT-calculated energy barriers. This indicates that CO2 conversion and methanol selectivity over the (111) surface can be further enhanced if homolytic H2 dissociation can be accelerated for instance by introducing transition metal dopants as already shown by some experimental observations.

Mechanism investigation and catalyst screening of high-temperature reverse water gas shift reaction

Reverse water gas shift (RWGS) catalysis, a prominent technology for converting CO2 to CO, is emerging to meet the growing demand of global environment. However, the fundamental understanding of the reaction mechanism is hindered by the complex nature of the reaction. Herein, microkinetic modeling of RWGS on different metals (i.e., Co, Ru, Fe, Ni, Cu, Rh, Pd, and Pt) was performed based on the DFT results to provide the mechanistic insights and achieve the catalyst screening. Adsorption energies of the carbon-based species and the oxygen-based species can be correlated to the adsorption energy of carbon and oxygen, respectively. Moreover, oxygen adsorption energy is an excellent descriptor for the barrier of CO2 and CO direct dissociation and the difference in reaction barrier between CO2 (or CO) dissociation and hydrogenation. The reaction mechanism varies on various metals. Direct CO2 dissociation is the dominating route on Co, Fe, Ru, Rh, Cu, and Ni, while it competes with the COOH-mediated path on Pt and Pd surface. The eights metals can be divided into two groups based on the degree of rate control analysis for CO production, where CO–O bond cleavage is rate relevant on Pt, Pd, and Cu, and OH–H binding is rate-controlling on Co, Fe, Ru, Ni, and Rh. Both CO-direct dissociation and hydrogen-assisted route to CH4 contribute to the methane formation on Co, Fe, Pt, Pd, Ru, and Rh, despite the significant barrier difference between the two routes. Besides, the specific rate-relevant transition states and intermediates are suggested for methane formation, and thus, the selectivity can be tuned by adjusting the energy. The descriptor (C- and O- formation energy) based microkinetic modeling proposed that the activity trend is Rh~Ni > Pt~Pd > Cu > Co > Ru > Fe, where Fe, Co, Ru, and Ni tends to be oxidized. The predicted activity trend is well consistent with those obtained experimentally. The interpolation concept of adsorption energy was used to identify bimetallic materials for highly active catalysts for RWGS.

Mechanistic Study of Catalase- and Superoxide Dismutation-Mimic Activities of Cobalt Oxide Nanozyme from First-Principles Microkinetic Modeling

Cobalt oxide (Co3O4) has attracted considerable interest because of its high catalytic activity, especially for intrinsic catalase (CAT)-mimic and superoxide dismutation (SOD)-mimic activities. However, understanding of its catalytic mechanism from atomic or molecular level remains limited. Here, we propose base-like dissociative, acid-like dissociative and bi-hydrogen peroxide associative mechanisms of CAT-mimic activity, Langmuir–Hinshelwood (LH) and Eley–Rideal (ER) mechanisms of SOD-mimic activity on cobalt oxide surface with atomistic thermodynamic and kinetic details by a combination of rigorous density functional theory and microkinetic modeling. The catalytic activity of Co3O4 depends strongly on their size and structure. In this study, Co3O4 nanozyme with different size and structure exhibited different catalytic activities in the order of (Co3O4)2 > (Co3O4)3 > Co3O4. This order is closely related to their weak, tunable Co–O bonds. Our microkinetic modeling analysis shows that bi-hydrogen peroxide associative mechanisms (mechanism C) of CAT-mimic activity and ER mechanism of SOD-mimic activity for (Co3O4)2 are favorable, which is identified by the rate-determining steps (RDS), Energy span model (ESM), and microkinetic modeling analysis. For the CAT-mimic activities on (Co3O4)n surface, Campbell’s degree of rate control analysis indicates the key to catalyst improvement and design is to stabilize the key steps, which are related to the formation of H2O molecular. For the SOD-mimic activities of (Co3O4)n, we find the formation of H2O2 molecular to be the sole rate-controlling step. Degree of the thermodynamic rate control analysis reveals that the stronger H2O2*, OH* binding would facilitate the reaction of CAT-like activities of (Co3O4)n. And the adsorbed OHOO* with large negative degree of thermodynamic rate control would inhibit the reaction of CAT-like activities of (Co3O4)n. Our results have not only provided new insights into deciphering (Co3O4)n artificial enzymes, but will also facilitate the design and construction of other types of target-specific artificial enzymes.

Surface reaction kinetics of methane oxidation over PdO

A two-site mean field extended microkinetic model was developed based on DFT data to investigate the methane oxidation reaction over PdO(1 0 1) for environmental applications at atmospheric to moderate pressures, fuel-lean and low-temperature model exhaust gas conditions. The mechanism includes various carbonaceous pathways for methane oxidation together with lattice oxygen vacancy formation via Mars-van-Krevelen steps. The mechanism was compared with catalytic light-off curves (573–823 K) on a Pd/Al2O3 coated on monolith for CH4/O2/H2O/N2 mixtures with 1000 ppm CH4, 10 vol% O2 at varying H2O feed concentration (0–12 vol%) and pressure (1–4 bar). The mechanism was demonstrated to quantitatively reproduce experimental light-off curves for dry and wet feeds and capture the water inhibition phenomena, when catalyst deactivation and/or particle size dependent kinetic effects are taken into account. A degree of rate control analysis reveals dissociative CH4 adsorption via hydrogen abstraction over Pdcus-Ocus site-pairs as the major rate controlling step during light-off. Supplementary in situ DRIFTS investigations analyzed for dry and wet reactive gas-mixtures containing different types of C1-fuels, namely methane, methanol and formic acid were conducted to identify surface species during catalytic methane oxidation and hydroxide formation.

First-Principles and Microkinetic Simulation Studies of the Structure Sensitivity of Cu Catalyst for Methanol Steam Reforming

High CO2 and H2 selectivity are important issues for methanol steam reforming (MSR) to provide H2 as a clean energy carrier. The structure sensitivity and the factors governing the activity and selectivity for MSR on Cu catalysts are systematically investigated using density functional theory calculations and microkinetic simulation. Potential energy surfaces including water dissociation, methanol dehydrogenation, formaldehyde desorption and coupling with oxygen-containing intermediates, and formation of hydrogen and carbon dioxide are calculated over Cu(111), (100), (221), (211), and (110) surfaces, respectively. It is found that Cu(110) facet is the most active and selective toward carbon dioxide; Cu(221) is also active but highly selective toward formaldehyde, whereas Cu(111) is nearly inactive. Degree of rate control analysis shows that the activity is controlled mainly by methanol dehydrogenation to formaldehyde, whereas the degree of selectivity control shows that the selectivity toward formaldehyde...

Catalytic descriptors and electronic properties of single-site catalysts for ethene dimerization to 1-butene

Six first-row transition metal cations (Mn2+, Fe2+, Co2+, Ni2+, Cu2+, Zn2+) were evaluated as catalysts for ethene dimerization to 1-butene. This is an important reaction in the chemistry of CC bond formation and in the conversion of natural gas to higher hydrocarbons. Two related classes of transition metal cation catalysts were investigated: 1) single transition metal cations supported on zirconium oxide nodes of the metal–organic framework NU-1000 and 2) small metal hydroxide clusters with two metal atoms (M2) that could be grown by atomic layer deposition on a support exhibiting isolated hydroxyl groups. Using scaling relations, the free energies of co-adsorbed hydrogen and ethene (i.e., (H/C2H4)*) and adsorbed ethyl (i.e., C2H5*) were identified as descriptors for ethene dimerization catalysis. Using degree of rate control analysis, it was determined that the rate controlling steps are either ethene insertion (CC bond forming) or β-hydride elimination (CH bond breaking), depending on the metal. Using degree of catalyst control analysis, it was determined that activity on all the catalysts studied could be improved by tuning the free energy of C2H5*.

Hydrodeoxygenation of m-cresol over bimetallic NiFe alloys: Kinetics and thermodynamics insight into reaction mechanism

Developing mechanistic insights into the reaction network of hydrodeoxygenation (HDO) of lignin-derived compounds is key to rational design of high-performance catalysts for bio-oils upgrading. Herein, we present a comprehensive theoretical study on HDO of m-cresol, a model compound of phenolics, on Ni(1 1 1) and NiFe(1 1 1) surfaces using periodic density functional theory calculations and microkinetic modeling techniques, with a focus on the several competing reaction pathways including enol-keto tautomerization, hydrogenation, and dehydroxylation. Our results show that the activation of the COH bond of m-cresol and phenolic intermediates can be greatly promoted on oxophilic NiFe(1 1 1), evidenced by the elongated COH bond length and the enhanced dehydroxylation activity with respect to Ni(1 1 1). It is found that m-cresol HDO on NiFe(1 1 1) shares certain common features with that on Ni(1 1 1), but exhibits important differences that result in dramatic changes in selectivity. We show that the COH bond length of adsorbed phenolic intermediates can be used as a good descriptor for prediction on the COH bond scission reaction in HDO. Finally, microkinetic modeling augmented by degree of rate control analysis is applied to rationalize the experimentally-observed differences in product distributions over Ni and NiFe catalysts when kinetic factors still dominate.

Microkinetic Modeling of the Oxygen Evolution Reaction on Oxide Surfaces

The oxygen evolution reaction (OER) is an important anodic reaction that enables the sustainable production of H2 from water at ambient conditions via the hydrogen evolution reaction or provides protons for cathodic COxreduction reactions. Extensive density functional theory (DFT) calculations have been previously carried out to determine the theoretical limiting potential (where all steps are exergonic) of the OER as a function of binding energy descriptors. This work extends those analyses by feeding DFT calculated energies into a mean field, steady state microkinetic model of the OER. This model demonstrates that a simple mechanism consisting of four coupled proton electron transfers can be used to predict activity trends in relevant catalyst surfaces such as rutile and perovskite oxides. A potential dependent barrier is assumed for each coupled proton electron transfer step. The location of the peak of the volcano at OER relevant potentials agrees with thermodynamic predictions. A sensitivity analysis shows that the volcano shape and peak location is dependent on the assumed barrier and how it scales with potential. The peak location is robust for reasonable barrier assumptions at OER relevant potentials. A degree of rate control analysis is carried out to determine how the rate constants for each step affect the overall rate of reaction as a function of catalyst binding energies. Changes in tafel slope for a given surface have been observed experimentally for the OER. The model presented here predicts these changes and demonstrates that changes in tafel slope can be due to switches in reaction mechanism, coverage, and rate controlling step. Surface Pourbaix diagrams are traditionally used to predict equilibrium coverages. Surface kinetics must be considered to determine the surface coverage at the potentials where OER (a non-equilibrium process) is occurring. This research presents a method to determine the steady state coverage of catalyst surfaces under OER relevant conditions. In this method, a coverage is initially assumed based on a surface Pourbaix analysis. Intermediate free energies are calculated at the specified coverage using DFT and fed into the microkinetic model. If the steady-state coverage predicted by the microkinetic model is in agreement with the coverage used in the DFT calculations, the coverage is self consistent. If the kinetic model predicts a different coverage than that used to determine the energies, the calculations must be redone at the coverage predicted by the kinetic model until a self-consistent coverage is found. Generally, we find the steady state coverage corresponds to the precursor of the thermodynamically limiting step for potentials above the limiting potential. This analysis demonstrate that qualitative trends can be predicted by a simple model and assumed proton transfer barriers and demonstrates how factors such as barriers, potential scaling, and coverage affect reaction rate. Future work in determining electrochemical barriers and their potential dependence is necessary to quantitatively predict rates. Figure 1

Using degrees of rate control to improve selective n-butane oxidation over model MOF-encapsulated catalysts: sterically-constrained Ag3Pd(111).

Metal nanoparticles encapsulated within metal organic frameworks (MOFs) offer steric restrictions near the catalytic metal that can improve selectivity, much like in enzymes. A microkinetic model is developed for the regio-selective oxidation of n-butane to 1-butanol with O2 over a model for MOF-encapsulated bimetallic nanoparticles. The model consists of a Ag3Pd(111) surface decorated with a 2-atom-thick ring of (immobile) helium atoms which creates an artificial pore of similar size to that in common MOFs, which sterically constrains the adsorbed reaction intermediates. The kinetic parameters are based on energies calculated using density functional theory (DFT). The microkinetic model was analysed at 423 K to determine the dominant pathways and which species (adsorbed intermediates and transition states in the reaction mechanism) have energies that most sensitively affect the reaction rates to the different products, using degree-of-rate-control (DRC) analysis. This analysis revealed that activation of the C-H bond is assisted by adsorbed oxygen atoms, O*. Unfortunately, O* also abstracts H from adsorbed 1-butanol and butoxy as well, leading to butanal as the only significant product. This suggested to (1) add water to produce more OH*, thus inhibiting these undesired steps which produce OH*, and (2) eliminate most of the O2 pressure to reduce the O* coverage, thus also inhibiting these steps. Combined with increasing butane pressure, this dramatically improved the 1-butanol selectivity (from 0 to 95%) and the rate (to 2 molecules per site per s). Moreover, 40% less O2 was consumed per oxygen atom in the products. Under these conditions, a terminal H in butane is directly eliminated to the Pd site, and the resulting adsorbed butyl combines with OH* to give the desired 1-butanol. These results demonstrate that DRC analysis provides a powerful approach for optimizing catalytic process conditions, and that highly selectivity oxidation can sometimes be achieved by using a mixture of O2 and H2O as the oxidant. This was further demonstrated by DRC analysis of a second microkinetic model based on a related but hypothetical catalyst, where the activation energies for two of the steps were modified.