Hydrogenolysis Of Propane Research Articles

Applications of nickel-containing structured microfibrous catalysts for the process of propane hydrogenolysis

This work evaluates the possibility of using nickel-containing structured glass fiber catalysts (Ni/GFC) for the process of hydrogenolysis of gas condensate (GC) into transportable components of natural gas, which will increase the efficiency of GC processing and contribute to the development of more cost-effective technologies in the oil-gas industry. Ni/GFC samples with Ni content of 5, 10 and 15% wt. were synthesized by surface thermal synthesis (STS). An industrial granular catalyst with a mass Ni content of 16% was used to compare the catalytic activity of the obtained catalysts. The highest activity and selectivity of methane formation is observed on the 10% Ni/ GFC catalyst, by these parameters it is superior not only to other GFCs, but also the traditional granular catalyst.

Support induced effects on the activity and stability of Ga2O3 based catalysts for the CO2-assisted oxidative dehydrogenation of propane

The influence of the support nature (Al2O3, TiO2, SiO2) on the activity and stability of supported Ga2O3 (10 wt%) catalysts was investigated for the production of propylene through the CO2-assisted oxidative dehydrogenation of propane (CO2-ODP). Catalytic activity was found to be higher when gallium oxide was dispersed on alumina support which was characterized by the highest acid site density and moderate surface basicity. Below 650 °C propylene yield increased in the order Ga2O3-TiO2<Ga2O3-SiO2<Ga2O3-Al2O3, which was modified as Ga2O3-Al2O3<Ga2O3-TiO2<Ga2O3-SiO2 for higher reaction temperatures. Propylene selectivity decreased with increasing reaction temperature followed by an increase of ethylene and methane selectivity implying that the side reactions of propane hydrogenolysis and propane/propylene decomposition were facilitated at higher temperatures hindering the CO2-ODP reaction. Gallium oxide catalysts supported on TiO2 and SiO2 exhibited sufficient stability for 30-35 hours on stream at 660 and 710 οC, contrary to Ga2O3-Al2O3 which although was stable at 710 οC it was gradually deactivated when the reaction was taking place at 600 °C. Temperature programmed oxidation experiments showed that carbon deposition was favored over Ga2O3-Al2O3 catalyst when the reaction was conducted at low temperature, which may be related to the higher surface acidity of this sample and be responsible for its deactivation with time. SEM images and elemental mapping obtained from both the freshly prepared and used Ga2O3-MxOy samples showed that Ga and M (M: Si, Ti, Al) were uniformly present even after prolonged catalyst interaction with the reaction mixture. EDS analysis indicated that carbon formation was accelerated with increasing reaction temperature.

Demystifying group-4 polyolefin hydrogenolysis catalysis: Gaseous propane hydrogenolysis mechanism over the same catalysts

A kinetic/mechanistic investigation of gaseous propane hydrogenolysis over the single-site heterogeneous polyolefin depolymerization catalysts AlS/ZrNp2 and AlS/HfNp2 (AlS = sulfated alumina, Np = neopentyl), is use to probe intrinsic catalyst properties without the complexities introduced by time- and viscosity-dependent polymer medium effects. In a polymer-free automated plug-flow catalytic reactor, propane hydrogenolysis turnover frequencies approach 3,000 h-1 at 150 °C. Both catalysts exhibit approximately linear relationships between rate and [H2] at substoichiometric [H2] with rate law orders of 0.66 ± 0.09 and 0.48 ± 0.07 for Hf and Zr, respectively; at higher [H2], the rates approach zero-order in [H2]. Reaction orders in [C3H8] and [catalyst] are essentially zero-order under all conditions, with the former implying rapid, irreversible alkane binding/activation. This rate law, activation parameter, and DFT energy span analysis support a scenario in which [H2] is pivotal in one of two plausible and competing rate-determining transition states-bimolecular metal-alkyl bond hydrogenolysis vs. unimolecular β-alkyl elimination. The Zr and Hf catalyst activation parameters, ΔH‡ = 16.8 ± 0.2 kcal mol-1 and 18.2 ± 0.6 kcal mol-1, respectively, track the relative turnover frequencies, while ΔS‡ = -19.1 ± 0.8 and -16.7 ± 1.4 cal mol-1 K-1, respectively, imply highly organized transition states. These catalysts maintain activity up to 200 °C, while time-on-stream data indicate multiday activities with an extrapolated turnover number ~92,000 at 150 °C for the Zr catalyst. This methodology is attractive for depolymerization catalyst discovery and process optimization.

Multiscale modeling of hydrogenolysis of ethane and propane on Ru(0001): Implications for plastics recycling

Plastic waste presents an environmental threat. Chemical recycling via hydrogenolysis can convert plastic waste into waxes, lubricants, and fuels. Among catalysts, Ru stands out for its superior activity and selectivity. The chemistry of light alkane hydrogenolysis can help understanding plastics deconstruction. We perform first-principles calculations, develop descriptor-based relations, and conduct microkinetic modeling and analysis on ethane and propane. Predictions are in excellent agreement with experimental data. We identify a similar cracking pattern for both hydrocarbons entailing a deeply dehydrogenated species with the removal of four hydrogen atoms: CHCH* +* → 2CH* for ethane and CH3CCH* +2 * → CH3C* + CH* for propane. We find that the rate-determining step is the C-C cracking for ethane and the first dehydrogenation from the terminal carbon (CH3CH2CH3*+* → CH3CH2CH2*+H*) for propane. The vinyl species CH2CH* produced from propane cracking is responsible for whether a single or multiple cracking events occur and effectively controls the selectivity. Specifically, ethane formation in propane hydrogenolysis is suppressed at elevated temperatures due to over-cracking via multiple (two here) cracking events being preferred over hydrogenation and desorption of ethane from the catalyst. Our workflow and models provide a baseline for future studies on heavier hydrocarbons. Insights into recent experimental studies of polyethylene over Ru-based catalysts are discussed.

Assessment of metal-metal interactions and catalytic behavior in platinum-tin bimetallic subnanometric clusters by using reactive characterizations

Several reactive characterizations were used to study the effect that reduction duration of PtSn-K/MFI has on hydrocarbon catalysis, including propane dehydrogenation, propane hydrogenolysis, and ethane H/D exchange. Propane dehydrogenation results demonstrate that increased reduction time causes the PtSn-K/MFI to have higher selectivity towards propylene, lower rates of catalyst deactivation, and lower rates of dehydrogenation. Consistent with higher selectivity towards propylene with longer catalyst reduction times, slower rates of hydrogenolysis are also observed over a large range of H2:propane ratios. H/D exchange experiments to assess rates of C–H activation were carried out on PtSn-K/MFI by using ethane and D2, which demonstrate that longer reduction time significantly inhibits the rate of C–H activation on PtSn-K/MFI. The substantial effects observed by using reactive characterizations were difficult to be interpreted by more advanced characterization techniques such as EXAFS, because the structural changes of the PtSn nanoclusters are quite subtle. Indeed, in a previous report on the PtSn-K/MFI material, Pt and Sn EXAFS were statistically indistinguishable with different reduction times, illustrating that combining reactive characterizations, particularly with the application of H/D exchange, provides the ability to differentiate fundamental effects that impact catalyst performance. The importance of C–H activation was confirmed by isotopic experiments for propane dehydrogenation, which indicate that the first C–H activation step is rate-limiting during dehydrogenation, with a kinetic isotope effect of ∼2.5. These results together show that increased reduction time gives a catalytic material with superior catalytic properties (i.e. higher propylene selectivity and lower deactivation rates), and this is proposed to be due to increased platinum-tin interactions, which modifies and weakens hydrocarbon adsorption, thereby limiting strongly adsorbed intermediates that are precursors to hydrogenolysis products and coke.

Experimental verification of kinetics and internal diffusion impact on low temperature steam reforming of a propane-methane mixture over Ni-based catalyst

Experiments were made on three fractions (0.5–1, 2–2.5 and 3–5 mm) of a Ni/Cr2O3/Al2O3 catalyst in order to verify the kinetics and influence of internal diffusion transport on the apparent reaction rate of low-temperature steam reforming of a propane-methane mixture. Feed gas composition was: C3H8 = 22.6%, CH4 = 77.4%, H2O/C = 0.51, GHSV = 11600 h−1, temperature 300–370 °C. To analyze the experimental data, a plug-flow reactor model with fixed temperature profiles was used; the profiles were obtained by interpolating the measurements of a moving thermocouple placed along the axis of the catalyst bed. The global kinetic scheme included the parallel reactions of propane steam reforming and propane hydrogenolysis. The catalyst effectiveness factor was calculated with the effective diffusion coefficient based on the Wilke formula, Thiele modulus and experimental pore size distribution. Experimental data for all catalyst fractions are described well by the proposed model at a porous catalyst tortuosity factor 1.53 and permeability coefficient 0.26.

Strong metal-support interaction (SMSI) of Pt/CeO2 and its effect on propane dehydrogenation

Upon reduction at 975 °C, a strong metal-support interaction (SMSI) of CeO2 on Pt NPs leads to low rates for ethylene hydrogenation and propane dehydrogenation, but high olefin selectivity for the latter reaction. By contrast, reduction at 550 °C of Pt/CeO2, leads to 5 nm Pt NP’s with ethylene hydrogenation and propane dehydrogenation TORs and low olefin selectivity similar to Pt/SiO2. X-ray absorption fine structure (EXAFS) and scanning transmission electron microscopy (STEM) shows formation of ∼15 nm monometallic Pt nanoparticles partially covered by SMSI CeO2. The propylene selectivity of Pt NP’s covered by SMSI CeO2 was ∼95 % suggesting there were few Pt ensembles capable of catalysing propane hydrogenolysis; while the remaining exposed Pt remain active for dehydrogenation reactions.

Influence of the Catalyst Particle Size on the Aqueous Phase Reforming of n-Butanol Over Rh/ZrO2.

Butanol is a by-product obtained from biomass that can be valorized through aqueous phase reforming. Rh/ZrO2 catalysts were prepared and characterized, varying the size of the support particles. The results showed a relatively mild effect of internal mass transport on butanol conversion. However, the influence of internal transport limitations on the product distribution was much stronger, promoting consecutive reactions, i.e., dehydrogenation, hydrogenolysis, and reforming of propane and ethane. Hydrogen consuming reactions, i.e., hydrogenolysis, were more strongly enhanced than hydrogen producing reactions due to internal concentration gradients. Large support particles deactivated faster, attributed to high concentrations of butyraldehyde inside the catalyst particles, enhancing deposit formation via aldol condensation reactions. Consequently, also the local butyric acid concentration was high, decreasing the local pH, enhancing Rh leaching. The influence of internal transfer limitation on product distribution and stability is discussed based on a reaction scheme with three main stages, i.e., (1) formation of liquid intermediates via dehydrogenation, (2) formation of gas via decarbonylation/decarboxylation reactions, and (3) hydrocarbon hydrogenolysis/reforming/dehydrogenation.

Three‐step macrokinetic model of butane and propane steam conversion to methane‐rich gas

AbstractLow‐temperature steam conversion (LTSC) of a methane‐butane mixture (95% methane and 5% butane) into a methane‐rich gas over an industrial Ni‐based catalyst has been studied with the following reaction conditions: temperature 200–320°C, pressure 1 bar, gas hour space velocity 1200–3600 h–1, and steam to carbon ratio 0.64. A three‐step macrokinetic model has been suggested based on the kinetic parameters found. The model includes the following reactions: (1) irreversible steam reforming; (2) CO2 methanation, which occurs in a quasi‐equilibrium mode at temperatures above 260°C; (3) hydrogenolysis of propane and butane, which is essential at temperatures below 260°C. Steam reforming was shown to limit the overall reaction rate, whereas hydrogenolysis and CO2 methanation determined the product distribution in low‐ and high‐temperature regions, respectively. Temperature dependencies of the product distribution for the LTSC of a model ternary methane‐propane‐butane mixture (85% methane, 10% propane, and 5% butane) have been successfully simulated using the three‐step model suggested.

Mechanistic studies through H–D exchange reactions: Propane aromatization in HZSM5 and Ga/HZSM5 catalysts

HZSM5 and Ga/HZSM5 catalysts were studied in propane H–D isotopic exchange at various temperatures and D2 gas partial pressures. Stepwise and multiple exchange were observed on both the pure zeolite and the Ga/HZSM5 catalyst. Initial product distribution simulations by a Monte Carlo algorithm showed that three processes were necessary to explain the observed patterns in all catalysts: one stepwise and two multiple exchange processes, where one of the multiple exchange processes was observed only on Ga/HZSM5. Almost all processes were negatively influenced by D2 partial pressure, indicating competition with propane for the active sites. Reaction mechanisms and intermediate species were proposed for all processes discussed. In the simultaneous H–D exchange and aromatization/hydrogenolysis reactions, it was observed that aromatics were produced after several dehydrogenation–oligomerization–cracking cycles, while methane and ethane were formed mainly by direct propane hydrogenolysis on the Ga+/GaH2+ pair.

Process for methanol coupled catalytic cracking reaction of naphtha using a modified ZSM-5 molecular sieve catalyst

HZSM5 and Ga/HZSM5 catalysts were studied in propane H–D isotopic exchange at various temperatures and D2 gas partial pressures. Stepwise and multiple exchange were observed on both the pure zeolite and the Ga/HZSM5 catalyst. Initial product distribution simulations by a Monte Carlo algorithm showed that three processes were necessary to explain the observed patterns in all catalysts: one stepwise and two multiple exchange processes, where one of the multiple exchange processes was observed only on Ga/HZSM5. Almost all processes were negatively influenced by D2 partial pressure, indicating competition with propane for the active sites. Reaction mechanisms and intermediate species were proposed for all processes discussed. In the simultaneous H–D exchange and aromatization/hydrogenolysis reactions, it was observed that aromatics were produced after several dehydrogenation–oligomerization–cracking cycles, while methane and ethane were formed mainly by direct propane hydrogenolysis on the Ga+/GaH2+ pair.

New insights into structure–activity relationships for propane hydrogenolysis over Ni–Cu bimetallic catalysts

The structure–activity relationships of Cu–Ni bimetallic catalysts in propane hydrogenolysis reactions were investigated by using model catalyst systems.

Effect of pre-reduction on the performance of Fe2O3/Al2O3 catalysts in dehydrogenation of propane

The effect of carbon monoxide and hydrogen pre-reduction on the performance of 10FeAl catalyst in propane dehydrogenation was studied. The optimal results, 20wt% propylene yield at an overall propane conversion of 24wt% was obtained over the sample pre-reduced by hydrogen at 600°C for 10h at 560°C. Based on XRD, XPS and IR results, it is proposed that the carbon and FexC species formed from propylene cracking under the activation of surface adsorbed oxygen species are the active sites for the formation of abundant methane over untreated 10FeAl catalyst. Pre-reduction treatment leads to the consumption of surface adsorbed oxygen species and the formation of Fe and Fe2+ species, which are active for propane dehydrogenation. For one thing, propane hydrogenolysis is strongly inhibited due to the large size (around 30nm) of Fe grains. For another, propylene cracking and the generation of carbon and FexC species are largely suppressed in the absence of surface electronegative oxygen species, hence inhibiting propane cracking and hydrogenolysis reactions, resulting in greatly improved dehydrogenation performance.

Modifying structure-sensitive reactions by addition of Zn to Pd

Silica-supported Pd and PdZn nanoparticles of a similar size were evaluated for neopentane hydrogenolysis/isomerization and propane hydrogenolysis/dehydrogenation. Monometallic Pd showed high neopentane hydrogenolysis selectivity. Addition of small amounts of Zn to Pd lead Pd–Zn scatters in the EXAFS spectrum and an increase in the linear bonded CO by IR. In addition, the neopentane turnover rate decreased by nearly 10 times with little change in the selectivity. Increasing amounts of Zn lead to greater Pd–Zn interactions, higher linear-to-bridging CO ratios by IR and complete loss of neopentane conversion. Pd NPs also had high selectivity for propane hydrogenolysis and thus were poorly selective for propylene. The PdZn bimetallic catalysts, however, were able to preferentially catalyze dehydrogenation, were not active for propane hydrogenolysis, and thus were highly selective for propylene formation. The decrease in hydrogenolysis selectivity was attributed to the isolation of active Pd atoms by inactive metallic Zn, demonstrating that hydrogenolysis requires a particular reactive ensemble whereas propane dehydrogenation does not.

Fibrous Nano-Silica Supported Ruthenium (KCC-1/Ru): A Sustainable Catalyst for the Hydrogenolysis of Alkanes with Good Catalytic Activity and Lifetime

We have shown that fibrous nanosilica (KCC-1) can serve as a suitable support for the synthesis of highly dispersed ruthenium (Ru) nanoparticles. The resulting KCC-1/Ru catalyst displayed superior activity for the hydrogenolysis of propane and ethane at atmospheric pressure and at low temperature. The high catalytic activity was due to the formation of Ru-nanoparticles with an active size range (1–4 nm) and the presence of hexagonal-shaped particles with several corners and sharp edges possessing reactive atoms with lowest coordination numbers. The catalyst was stable with an excellent lifetime and no sign of deactivation, even after eight days. This enhanced stability may be due to the fibrous nature of KCC-1 which restricts Ostwald ripening of Ru nanoparticles.

Dehydrogenation of Propane to Propylene over Supported Model Ni–Au Catalysts

Hydrogenolysis and dehydrogenation of propane were studied over model nickel–gold catalysts. The supported model Ni–Au catalysts were prepared by depositing Ni and Au onto a planar silica film. Infrared reflection absorption spectroscopic data showed that isolated Ni sites appeared and became dominant on the surface with the addition of Au to Ni. For the conversion of propane in the presence of hydrogen, the dehydrogenation of propane to propylene was observed on the Ni–Au bimetallic catalysts, whereas only hydrogenolysis products were observed on the monometallic Ni catalyst. A correlation was found between the concentration of isolated Ni sites and the catalytic activity for propane dehydrogenation.

ChemInform Abstract: Hydrogenation of Alkanes. Part 8. Hydrogenolysis of Propane, n-Butane and Isobutane on Rhenium/Alumina Catalysts.

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Propane Aromatization on Zn-Modified Zeolite BEA Studied by Solid-State NMR in Situ

The conversion of propane (propane-1-13C and propane-2-13C) on Zn/H-BEA zeolite at 520−620 K has been studied by 1H and 13C (CP) MAS NMR. Propene adsorption complex with zinc sites (π-complex) and σ-allylzinc species as intermediates have been identified in the course of propane conversion to aromatics. The mechanism leading to the formation of methane and ethane, which are constituents of an undesirable route in propane conversion, has been examined by kinetic modeling of the expected reaction network based on in situ 1H MAS NMR kinetic measurements of the reaction performance. The pathways for propane aromatization and hydrogenolysis have been proposed. Hydrogenolysis of propane has been concluded to occur with the involvement of both Bronsted acid sites and Zn sites.

Modelling alkane hydrogenolysis: identification of conditions for surface polymer formation

Results of a wide-ranging study of the kinetics of propane and n-butane hydrogenolysis on Ru/Al2O3 and K-promoted Ru/Al2O3 are analysed to establish the conditions of temperature and H2 pressure in which formation of unreactive ‚carbon’ vitiates efforts to develop a simple reaction model. These conditions occur at low H2 pressures (<0.16 atm) and are signalled by (i) deactivation that occurs with ‚standard’ reaction pulses and (ii) changes in the sense of product selectivity variation, as H2 pressure is altered. Treatment of Ru/Al2O3 by oxidation and low-temperature reduction lowers ‚carbon’ formation; so does promotion by K. The product selectivity changes strongly suggest that deactivation is caused by the polymerisation of adsorbed C1 species when too few H atoms are present to convert them to methane.

Effect of Na Addition on Catalytic Performance of PtSn/ZSM-5 Catalyst for Propane Dehydrogenation

Abstract PtSnNa/ZSM-5 catalysts with different amounts of Na were prepared by the sequential impregnation method on HZSM-5 zeolites, and their catalytic activities and stabilities in propane dehydrogenation were investigated. The effect of the addition of sodium on the physicochemical properties was studied by means of XRD (X-ray diffraction), IR spectrum of adsorbed pyridine, NH 3-TPD, H 2 chemisorption, TPR (temperature-programmed reduction), etc. The results indicated that the addition of Na had an obvious impact on the catalytic performance of the PtSn/ZSM-5 catalyst. A suitable concentration of Na could not only reduce the Brönsted acid sites and moderate/strong Lewis acid sites, thus preventing the catalyst from coking and improving the catalytic stability, but also increase the fraction of bare metallic Pt on the surface of the catalyst, thus increasing the catalytic activity. It was found that the propene selectivity and yield could reach the maximum, when the Na content was 1.0%. After reaction for 30 h, the propane conversion was still high (36.4%). However, the continuous addition of Na increased the weak Lewis acid sites and promoted the tin species to be reduced to metallic tin. In this instance, the cracking and hydrogenolysis of propane could be carried out easily, which was disadvantageous to the dehydrogenation.