Propene Formation Research Articles

Origin of Performances of Pt/Cu Single-Atom Alloy Catalysts for Propane Dehydrogenation

The propane dehydrogenation (PDH) reaction converts cheap propane to value-added propene. Pt-based catalysts show high performance in PDH, but suffer from coke formation and deactivation. Therefore, promoter, that is, a second metal component, is required to enhance its stability. Our previous study has constructed Pt/Cu single atom alloy (SAA) catalysts and achieved high PDH selectivity and anticoke ability. However, the nature of its high performance in PDH still remains to be revealed. This paper describes the origin of catalytic performance for Pt/Cu SAA in PDH via density functional theory (DFT) calculations and kinetic Monte Carlo (kMC) simulations. We constructed a complex reaction network with 54 reversible reaction steps, including adsorption, desorption, C–H bond breaking, and C–C bond cracking processes on the Pt/Cu SAA catalyst. The high selectivity of propene has been demonstrated because of the higher occurrence of propene formation and, simultaneously, the high energy barriers for deep dehydrogenation of propene. The lower coverages of the coke species origin from the deep dehydrogenation instead of the C–C bond cracking for Pt/Cu SAA catalyst, which is different from that proposed for Pt catalyst. The simulation suggests that hydrogen (H2) cofeeding can further reduce the surface coke species. Overall, the current study provides fundamental insights into the origin of high selectivity and anticoke ability to help the design of stable and high-performance Pt-based catalysts.

Identification of a Selectivity Descriptor for Propane Dehydrogenation through Density Functional and Microkinetic Analysis on Pure Pd and Pd Alloys

First principles periodic density functional theory (DFT) calculations, in conjunction with detailed microkinetic modeling and experimental characterization, are employed to elucidate the structure sensitivity and identify key selectivity descriptors for nonoxidative propane dehydrogenation (PDH) on intermetallic alloys. A comprehensive theoretical treatment of 1:1 PdIn surfaces demonstrates that the Pd-terminated steps have 5 orders of magnitude higher rates than do the (110) terraces, with nearly complete selectivity to propylene formation. Pure Pd steps and terraces, in contrast, have considerably lower propylene selectivity and higher coverages of adsorbed intermediates, suggesting that Pd may experience more coking and reduced lifetimes compared to the alloys. A degree of rate and selectivity control analysis on the optimized microkinetic model demonstrates that propane C–H bond scission to yield 1-propyl is the most kinetically relevant step for propylene formation, while the C–C bond breaking barriers are important for byproduct formation. From these analyses, a simplified rate expression is derived for the step surface of the alloy, leading to the identification of a selectivity descriptor expressed in terms of effective free energy barriers of the rate controlling transition states, propane C–H bond breaking, and propyne C–C bond breaking. This descriptor is subsequently generalized to evaluate the propylene production selectivities for a series of Pd-containing alloys. The results show enhanced agreement with experimentally measured selectivity trends compared to traditional selectivity descriptors, suggesting a general strategy for identification of highly selective, nonoxidative PDH alloy catalysts.

Impact of Adding Polysaccharides on the Stability of Egg Yolk/Fish Oil Emulsions under Accelerated Shelf-Life Conditions.

Polysaccharides can form interfacial complexes with proteins to form emulsions with enhanced stability. We assessed the effect of adding gum guar or gum arabic to egg yolk/fish oil emulsions. The emulsions were produced using simple or high-pressure homogenization, stored for up to 10 days at 45 °C, and characterized for their particle size and distribution, viscosity, encapsulation efficiency, oxidative stability, and cytotoxicity. Emulsions containing gum guar and/or triglycerides had the highest viscosity. There was no significant difference in the encapsulation efficiency of emulsions regardless of the polysaccharide used. However, emulsions containing gum arabic displayed a bridging flocculation effect, resulting in less stability over time compared to those using gum guar. Emulsions produced using high-pressure homogenization displayed a narrower size distribution and higher stability. The formation of peroxides and propanal was lower in emulsions containing gum guar and was attributed to the surface oil. No significant toxicity toward Caco-2 cells was found from the emulsions over time. On the other hand, after 10 days of storage, nonencapsulated fish oil reduced the cell viability to about 80%. The results showed that gum guar can increase the particle stability of egg yolk/fish oil emulsions and decrease the oxidation rate of omega-3 fatty acids.

Experimental Study of Coflow Propane—Air Laminar Diffusion Flames at Subatmospheric Pressures

The effect of pressure on the flame’s physical structure and soot formation of the coflow propane—air laminar diffusion flames was studied experimentally at subatmospheric pressures from 30 to 101 kPa. Flames with a constant fuel mass flow rate combined with two different coflow air mass flow rates were investigated at different pressures. The spatially resolved relative soot volume fraction was measured using the laser-induced incandescence (LII) method. The height of the visible flame decreased moderately as the pressure (p) reduced from 101 to 30 kPa. The maximum flame diameter increased proportionally to pn, where the exponent changed from −0.4 to −0.52 as the air-to-fuel velocity ratio decreased from 1.0 to 0.5. Strong pressure dependence of the maximum relative soot volume fraction and the normalized maximum soot mass flow were observed and could be described by a power law relationship. However, a nonmonotonic dependence of soot formation on the air-to-fuel velocity ratio was observed at all the considered pressures.

The role of the compositions of HZSM-5 zeolites modified with nanosized anatase in propane and ethanol conversion

For the first time catalytic systems based on HZSM-5 zeolites (Si/Al=12, 25, 40) with nanosized anatase (NA) were obtained in situ by a modified hydrothermal method and a sol-gel method. Initial HZSM-5 and NA/HZSM-5 were characterized (XRPD, XAS, FT-IR, DSC, BET, XPS, SEM, TPD) and analyzed in the reactions of propane (liquefied petroleum gas) conversion (РС; temperature range 200–870 °С) with the formation of the main products propylene (C3H6, PP) and ethylene (C2H4, ETH) and liquid ethanol conversion (EC; temperature range 150–360 °C) with the formation of diethyl ether ((C2H5)2O, DEE) and ETH. In the PC reaction the maximum selectivity (SETH = 75%) and conversion (αP = 65%) were obtained on HZSM-5(40) (650 °С). With an increase in the NA content in NA/HZSM-5 SETH value increases up to 85%. In the EC reaction SDEE/ETH~98–99% was reached on HZSM-5(25) (200 °C) and HZSM-5(40) (300 °C); the αE to ETH is comparable (94%) for all HZSM-5 (300 °C). Modification of HZSM-5 with NA leads to a shift in the EC reaction temperature to lower temperature region (αE to ETH ~98% at 280 °C) with SDEE/ETH~94–100% for NA/HZSM-5(25) and NA/HZSM-5(12) obtained by a modified hydrothermal method. It was established the relationship between HZSM-5 and NA/HZSM-5 catalytic activity and their characteristics: Si/Al, NA content and Ti coordination number (NA/HZSM-5), the content of "zeolite water" with OH groups, specific surface area, meso- and micropores volume and spherical particles size (HZSM-5), surface energy of adsorption centers (HZSM-5 and NA/HZSM-5), and hence the content of acid sites, the strength of which is also determined by the temperature of the catalytic reaction. The reaction mechanisms have been presented. The obtained NA/HZSM-5 catalysts have a higher or comparable catalytic activity to commercial ones, but low cost, ease of preparation, and versatility.

Coupling of propane with CO2 to propylene over Zn-promoted In/HZSM-5 catalyst

The ZnIn/HZSM-5 catalyst was prepared by the wetness impregnation method, and the structure of catalyst was characterized by XRD, SEM, TEM, H2-TPR, NH3-TPD, XPS, TG, and N2 adsorption–desorption and then investigated in the coupling of propane with CO2 to propylene. It is found that the addition of Zn species is beneficial to the dispersion of In2O3 over HZSM-5, which plays an important role in propene formation, and adjusts the acidity distribution of In/HZSM-5 catalyst, as well as significantly improves the activity of In/HZSM-5 catalyst. The selectivity of propylene is 68.21% in the coupling of propane with CO2 over ZnIn/HZSM-5 catalyst when the time on stream (TOS) is 2 h, reaction temperature is 580 °C, reaction pressure is 0.3 MPa, C3H6:CO2:N2 = 1:4:5, catalyst mass is 0.2 g, and space velocity is 6000 mL gcat−1 h−1. However, the selectivity of propylene is only 63.33% and 0.25% in the propane dehydrogenation or CO2 hydrogenation reaction, respectively. The ZnIn/HZSM-5 catalyst showed a higher stability with only 0.80% conversion drop after three cycles.

Reactive interaction of isopropanol with Co3O4(1 1 1) and Pt/Co3O4(1 1 1) model catalysts

The structure and chemical composition of the catalyst may change under reaction conditions resulting in changes of the active sites and, thereby, loss of selectivity. In this work, we investigated the reactive interaction of isopropanol with well-defined Co3O4(111)/Ir(100) and Pt/Co3O4(111)/Ir(100) model catalysts by means of synchrotron radiation photoelectron spectroscopy (SRPES), near ambient pressure X-ray photoelectron spectroscopy (NAP−XPS), scanning tunneling microscopy (STM), and temperature programmed desorption (TPD). We found that adsorption at 150 K yields molecularly adsorbed isopropanol on both model catalysts accompanied by small fractions of isopropoxide and enolate species on Co3O4(111) and supported Pt nanoparticles, respectively. The reactive interaction of isopropanol-derived species with the model catalysts upon annealing in UHV and in 1×10-7 mbar and 1 mbar of isopropanol results in the reduction of Co3O4(111) followed by its conversion to CoO(111) and, finally, to metallic Co and Pt–Co alloy. The mechanism of isopropanol decomposition reveals remarkable sensitivity to the oxidation state and morphology of the model catalysts. On as-prepared Pt/Co3O4(111) catalyst, Pt particles densely cover the Co3O4(111) substrate steering isopropanol decomposition to acetone and hydrogen. Selective channels towards acetone and propene, both accompanied by water, open after temperature-driven sintering of the supported Pt particles. The selectivity of these channels is controlled by the degree of reduction of the Co3O4(111) substrate and the chemical composition of the supported nanoparticles. At high degrees of reduction of Co3O4(111), the formation of both propene and acetone through selective channels decline due to the strong preference for C–C bond scission. Under NAP conditions, the formation of acetone resumes after complete reduction of model catalysts to metallic Co and Pt–Co alloy.

Mechanistic insights into the conversion of dimethyl ether over ZSM-5 catalysts: A combined temperature-programmed surface reaction and microkinetic modelling study

The rates of adsorption, desorption, and surface reaction of dimethyl ether (DME) to olefins over fresh and working ZSM-5 catalysts with different Si/Al ratios (36 and 135) were decoupled using a combination of temperature-programmed surface reaction experiments and microkinetic modelling. Transient reactor performance was simulated by solving coupled 1D nonlinear partial differential equations accounting for elementary steps during the induction period based on the methoxymethyl mechanism on the zeolite catalyst and axial dispersion and convection in the reactor. Propylene is the major olefin formed, and site-specific scaling relations between the activation energies of DME desorption and barriers to the formation of methoxymethyl and methyl propenyl ether are observed. Six ensembles of sites are observed with a maximum of three adsorption/desorption sites and three adsorption/desorption/reaction sites. Barriers are generally higher for working catalysts than fresh catalysts. Activation energies of propylene formation of ca. 200 kJ mol−1 are obtained, corroborating direct mechanistic proposals.

Enhanced performances of bimetallic Ga-Pt nanoclusters confined within silicalite-1 zeolite in propane dehydrogenation

Ga-based catalysts are promising for use in propane dehydrogenation (PDH) because of the relatively superior activity, but the conventional Ga-based catalysts usually suffer from serious deactivation and unsatisfactory propene selectivity. Here, ultrafine bimetallic Ga-Pt nanocatalysts encapsulated into silicalite-1 (S-1) zeolites (GaPt@S-1) were synthesized by a facile ligand-protected direct H2-reduction method. It is indicated that this catalyst is composed of confined ultra-small GaPt alloy nanoclusters and a part of isolated tetrahedral coordination of Ga species. The confined GaPt alloy nanoclusters are the active sites for PDH reaction, and their high electron density could boost the desorption of products, resulting in a high propene selectivity of 92.1% and propene formation rate of 20.5 mol g−1Pt h−1 at 600 °C. Moreover, no obvious deactivation was observed over GaPt@S-1 catalyst even after 24 h on stream at 600 °C, affording an extremely low deactivation constant of 0.0068 h−1, which is much lower than that of the conventional Ga-based catalysts. Notably, the restriction of the zeolite can enhance the regeneration stability of the catalyst, and the catalytic activity kept unchanged after four consecutive cycles.

Methanol-to-olefin conversion over ZSM-5: influence of zeolite chemical composition and experimental conditions on propylene formation

The transformation of methanol into light olefins over ZSM-5 zeolites with different SiO2/Al2O3 molar ratios (SAR) and phosphorus contents was investigated. An increase in the SAR and amount of incorporated phosphorus reduced the acid-site strength and density, which favored catalytic stability and the production of light olefins, mainly propylene. Under an isoconversion of 91%, high propylene/ethylene molar ratios were observed using the zeolite with the highest SAR (i.e., HZ(280)) and the one containing 4 wt.% P (i.e., 4PHZ(30)). However, the latter was less stable when used in a long-term reaction. An experimental design was employed to investigate how the reaction temperature and methanol partial pressure affect the propylene (C3 =) yield in the reaction catalyzed by the HZ(280) zeolite, which led to a temperature of 475 °C and a methanol partial pressure of 0.04 atm using the proposed model within the experimental design space.

Substitution Reactions in the Pyrolysis of Acetone Revealed through a Modeling, Experiment, Theory Paradigm

The development of high-fidelity mechanisms for chemically reactive systems is a challenging process that requires the compilation of rate descriptions for a large and somewhat ill-defined set of reactions. The present unified combination of modeling, experiment, and theory provides a paradigm for improving such mechanism development efforts. Here we combine broadband rotational spectroscopy with detailed chemical modeling based on rate constants obtained from automated ab initio transition state theory-based master equation calculations and high-level thermochemical parametrizations. Broadband rotational spectroscopy offers quantitative and isomer-specific detection by which branching ratios of polar reaction products may be obtained. Using this technique, we observe and characterize products arising from H atom substitution reactions in the flash pyrolysis of acetone (CH3C(O)CH3) at a nominal temperature of 1800 K. The major product observed is ketene (CH2CO). Minor products identified include acetaldehyde (CH3CHO), propyne (CH3CCH), propene (CH2CHCH3), and water (HDO). Literature mechanisms for the pyrolysis of acetone do not adequately describe the minor products. The inclusion of a variety of substitution reactions, with rate constants and thermochemistry obtained from automated ab initio kinetics predictions and Active Thermochemical Tables analyses, demonstrates an important role for such processes. The pathway to acetaldehyde is shown to be a direct result of substitution of acetone's methyl group by a free H atom, while propene formation arises from OH substitution in the enol form of acetone by a free H atom.

ПЕРЕРАБОТКА СЖИЖЕННОГО НЕФТЯНОГО ГАЗА НА МОНО- И БИМЕТАЛЛИЧЕСКИХ КАТАЛИЗАТОРАХ

The reserves of liquefied petroleum gas in the production zones and fields are briefly characterized in present paper. The scope of liquefied petroleum gases application, catalytic transformation and their importance in obtaining products are described. Widespread use of nanostructured and nanoscale catalysts in catalysis processes and their properties are given in literature review. Chemical transformations of С3-С4-alkanes in the presence of mono- and bimetallic catalysts based on Cr/SiO2 are studied. By method of electron microscopy, it was determined that various highly dispersed oxides of chromium in lanthanum – modified catalyst interact with each other and with carrier. According to electronic paramagnetic resonance data, chromium is contained in a five- and three-valence state. Mono - and bimetallic catalysts were studied by physical and chemical methods: IR spectroscopy, electron microscopy (EM) using micro diffraction, EPR. Monometallic catalysts with a chromium content of 2-10 wt. % and bimetallic lanthanum-chromium-containing catalyst in the form of 5% La-Cr/SiO2 in a ratio of 1/1 were prepared in the work; the process temperature was varied in the range of 400 to 650°С. Introduction of lanthanum leads to the formation of LaCrO3, LaCrO4 compounds with low activity in dehydro-genation reaction of C3-C4 – alkanes. The maximum yield of C2-C4-olefins - 39.2%, i.e. the formation of propylene in high doses was observed in the presence of 5% Cr/SiO2.

THE ACTIVITY OF MOLYBDENE-VANADIUM OXIDE CATALYSTS IN THE ISOPROPYL ALCOHOL CONVERSION REACTION

The activity of molybdenum-vanadium oxide catalysts in the conversion of isopropyl alcohol has been studied. It was found that acetone and propylene are the main products of the isopropyl alcohol conversion reaction. Studies have shown that the activity of binary molybdenumvanadium oxide catalysts depends both on the reaction conditions and on the atomic ratio of molybdenum to vanadium. It has been shown that molybdenum-vanadium oxide catalysts have a sufficiently high activity in the reaction of propylene and acetone formation and can be used for further modification in order to increase their catalytic activity. Keywords: isopropyl alcohol, acetone, propylene, binary catalysts, molybdenum oxide, vanadium oxide.

Impact of Polyunsaturated Fatty Acid Dilution and Antioxidant Addition on Lipid Oxidation Kinetics in Oil/Water Emulsions.

As consumers increasingly demand "cleaner" labels, one available strategy is diluting oils high in unsaturated fatty acids into more stable, more saturated oils, thus delaying lipid oxidation by decreasing free-radical propagation reactions between oxidized fatty acids and unsaturated lipids. The effect of diluting fish oil into medium-chain triglycerides (MCTs) on oxidative stability was investigated using lipid hydroperoxides and gas chromatography headspace analysis. Dilutions up to 1 in 20 of fish oil in MCT extended propanal formation from 1 to 6 days in Tween-80-stabilized oil-in-water emulsions. This protective effect was not observed in emulsions wherein the two oils were in separate droplets. Fish oil blended with high oleic sunflower oil (HOSO) also demonstrated a protective effect when the oils were in the same emulsion droplets but not in separate emulsion droplets. The present study indicates that dilution can be used to increase the oxidative stability of polyunsaturated fatty acids in oil-in-water emulsions.

Propane Dehydrogenation on Ga2O3-Based Catalysts: Contrasting Performance with Coordination Environment and Acidity of Surface Sites

α-Ga2O3, β-Ga2O3, and γ-Ga2O3 as well as the silica-supported catalysts γ-Ga2O3/SiO2, β-Ga2O3/SiO2, and Ga(NO3)3-derived Ga/SiO2 were prepared, characterized, and evaluated for propane dehydrogenation (PDH) at 550 °C. The coordination environment and acidity of surface sites in stand-alone and SiO2-supported Ga2O3 catalysts were studied using FTIR, 15N dynamic nuclear polarization surface-enhanced NMR spectroscopy (15N DNP SENS), and DFT modeling of the adsorbed pyridine probe molecule. The spectroscopic data suggest that the Lewis acidic surface Ga sites in γ-Ga2O3 and β-Ga2O3 (the latter obtained from colloidal nanocrystals of γ-Ga2O3 via thermal treatment at 750 °C) are similar, except that β-Ga2O3 contains a larger relative fraction of weak Ga3+ Lewis acid sites. In contrast, α-Ga2O3 features mostly strong Lewis acid sites. This difference in surface sites parallels their difference in catalytic activities: i.e., weak Lewis acid surface sites are more abundant in β-Ga2O3 relative to α-Ga2O3 and γ-Ga2O3 and the increased relative abundance of weak Lewis acidity correlates with a higher initial catalytic activity in PDH, 0.41 > 0.28 > 0.14 mmol C3H6 m–2 (Ga2O3) h–1 at 550 °C, for respectively β-, α-, and γ-Ga2O3 with initial propene selectivities of 86, 83, and 88%. Dispersion of γ-Ga2O3 or β-Ga2O3 on a silica support introduces strong as well as abundant weak Brønsted acidity to the catalysts, lowering the PDH selectivity. The γ-Ga2O3/SiO2 catalyst was slightly more active than β-Ga2O3/SiO2 in PDH (Ga normalized activity) with initial propene formation rates of 11 and 9 mol C3H6 mol Ga–1 h–1 (sel = 76 and 73%, respectively). However, these catalysts deactivated by ca. 55% within 100 min time on stream (TOS) due to coking. In contrast, Ga/SiO2, with mostly tetracoordinated surface Ga sites and abundant, strong Brønsted acid sites, gave a lower activity and selectivity in PDH (3.5 mol C3H6 mol Ga–1 h–1 and 49%, respectively) but showed no deactivation with TOS. DFT calculations using a fully dehydroxylated oxygen-deficient model β-Ga2O3 surface show that tetra- and pentacoordinated Ga Lewis acid sites bind pyridine more strongly than tricoordinated Ga sites and a higher relative fraction of strong Lewis acid sites correlates with increased coking. Overall, our results indicate that weakly Lewis acidic, tricoordinated Ga3+ sites are likely driving the superior PDH activity of β-Ga2O3.

Efficiency evaluation of using highly mineralized reservoir waters for preventing hydrate formation of natural gas in the conditions of Zakhidno-Radchenkivske gas-condensate field

A comparative analysis of hydrate formation inhibitors of different types: thermodynamic, anti-agglomerate, kinetic action was performed. The advantages and disadvantages of each class of reagents are considered. The possibility of using highly mineralized reservoir waters to prevent hydrate formation in gas condensate fields is proposed. Laboratory studies were conducted to determine the decrease in equilibrium temperature in the presence of reservoir water of the well 202 of Zakhidno-Radchenkivske gas-condensate field. Experimental determination of the equilibrium parameters of the hydrates formation of technical propane for the studied formation water showed that the value of ΔT is higher than predicted. This paradoxical effect can be explained by the multicomponent combination of formation water and, probably, the synergistic action of its micro-and macro components. The results of the calculation of the antihydrate properties of the reservoir water of Zakhidno-Radchenkivske gas-condensate field are presented. The results of industrial tests of using reservoir waters for the prevention of hydrate formation in the gas preparation system at Zakhidno-Radchenkivske gas-condensate field are presented. The results of industrial tests confirmed the effectiveness of the formation of reservoir water to prevent the formation of hydrates: hydrate formation in the well and on complex gas treatment unit was not detected. In addition, due to the use of well production, the cost of preparing gas for transportation has been significantly reduced. The article substantiates the possibility of using formation waters of oil and gas fields of the south-eastern part of the Dnieper-Donetsk basin as an inhibitor of hydrate formation.

Formation of ethane and propane via abiotic reductive conversion of acetic acid in hydrothermal sediments

Formation of ethane and propane via abiotic reductive conversion of acetic acid in hydrothermal sediments

Theoretical insight into the deoxygenation molecular mechanism of butyric acid catalyzed by a Ni12P6 cluster

For the deoxygenation of butyric acid catalyzed by Ni12P6 cluster, decreasing temperature is beneficial to butyraldehyde, n-butyl alcohol, and n-butane formation, and increasing temperature is preferable to propylene, propane, and butylene formation.

Kinetics of Propane Hydrate Formation from Melting Ice in Frozen Aqueous Poly(vinyl alcohol) Solutions

The kinetics of the formation of propane hydrates with the CsII crystal structure as one of the most common structures of hydrates of hydrocarbons, in frozen aqueous solutions was studied. The rate of the water transfer to propane hydrate in frozen aqueous poly(vinyl alcohol) solutions is many times higher than in common ice. The water transition to the liquid state upon hydrate formation in the course of ice melting in frozen aqueous poly(vinyl alcohol) solutions was studied by a NMR method. Microcrystals of propane hydrates formed in frozen aqueous poly(vinyl alcohol) solutions in the course of ice melting are smaller in size than the propane hydrate crystals formed in frozen water under equal conditions of hydrate formation.

Beyond the Reverse Horiuti–Polanyi Mechanism in Propane Dehydrogenation over Pt Catalysts

The catalytic dehydrogenation of light alkanes over Pt catalysts is generally accepted to follow a reverse Horiuti–Polanyi mechanism. Using a microkinetic analysis in combination with results from density functional theory calculations, we show that although propane dehydrogenation (PDH) occurs by two successive dehydrogenation steps on terraces, an unexpected non-reverse Horiuti–Polanyi mechanism accounts for more than half the propylene production at the under-coordinated active sites that dominate the kinetics of PDH. The main reaction is composed of three dehydrogenation steps that have two β-H atoms and one α-H atom removed from propane, followed by the hydrogenation of CH3CCH2; starting from this species, the formation of propylene and byproducts proceed by way of two parallel competing reactions. The proposed mechanism has been verified by exploring several key and general aspects of the kinetic behavior observed in the dehydrogenation of light alkanes, and it is found that only when adsorbate–adsorbate interactions are taken into consideration can the experimentally determined kinetics be properly reproduced. Increasing the H2 partial pressure from low values favors an increase in the coverage of free sites due to the gasification of adsorbed coke precursors, which in turn gives rise to lowered energy barriers for C–H bond breaking, thereby achieving an increased propane consumption rate. As the H2/C3H8 ratio increases, the rate of propylene production first goes up and then declines, and a maximum is observed at a H2/C3H8 ratio of 1.33, which occurs when the negative effect of the increased free 4-fold hollow sites that bring about deep dehydrogenation begins to dominate the positive effect of the increased free step sites that are responsible for activating propane. The mechanism formulated here proves to be valid even if the temperature, pressure, or the H2/C3H8 ratio is varied and hence provides a foundation for the rational design of metal and alloy catalysts for light alkane dehydrogenation.