H2 Pressure Research Articles

Consequences of metal-acid site proximity for alkane isomerization and β-scission mediated by bifunctional catalytic cascades

Bifunctional isomerization and β-scission of alkanes involve kinetic cascades mediated by alkenes that form at a (de)hydrogenation function that resides within diffusion distances from the acid function at which alkenes react. Such distances matter for reactivity and selectivity, especially within voids of molecular dimensions, because of gradients in reactant and product concentrations within acid domains. Dispersing Pt nanoparticles within zeolite crystals places the two functions within nanometer distances, instead of the larger distances prevalent when the Pt function resides outside zeolite crystals. Such intimacy leads to higher n-heptane conversion turnover rates (per H+) and shifts selectivities towards primary isoalkanes, most evidently on medium-pore zeolites (MFI), because confinement effects lead to slower diffusion and higher intrinsic H+ reactivity than in larger-pore zeolites, and for shorter Pt-H+ distances, which define the dimensions of the acid domain. Intracrystalline Pt nanoparticles do not affect the number or intrinsic properties of the metal or acid functions or introduce reaction channels mediated by more reactive (but less abundant) diene intermediates, as demonstrated here by reactive probes of metal (CO oxidation) and acid (CH3OH dehydration) functions, infrared spectra of OH groups and chemisorbed CO, kinetic effects of H2 pressures, and transition state energies from density functional theory. Metal-acid distances influence the requisite kinetic cascades instead through the formation and scavenging of reactants and intermediates along the isomerization-scission sequence in the presence of significant gradients in their concentrations. Reaction-transport treatments show that such gradients weaken with increasing intracrystalline densities of Pt nanoparticles (and consequent smaller acid domains), thus circumventing isoalkene equilibration and local thermodynamic bottlenecks through hydrogenation of the primary isoalkene products. Such scavenging inhibits the formation of dimethylpentenes, which act as required precursors to β-scission products, leading to higher selectivities to isoalkanes as Pt-H+ distances decrease. These data and reaction-transport formalisms resolve persistent controversies about the chemical or diffusional origins of rate and selectivity consequences of the location of a metal function. They demonstrate the essential, but often neglected, need to determine the precise location of the metal function and to develop reaction-transport treatments to describe rates and selectivity in bifunctional metal-acid catalysis.

Synthesis of Co―N―C catalysts from a glucose hydrochar and their efficient hydrogenation of nitrobenzene

A low-cost, green catalyst for nitrobenzene (NB) hydrogenation is needed for aniline production. We report the preparation of highly-dispersed Co particles supported on N-doped carbons by the hydrothermal treatment of glucose, followed by the pyrolysis of a mixture of urea, glucose hydrochar and cobalt nitrate in one-pot. The effect of the pyrolysis temperature on the microstructure of the catalysts was studied. Results indicated that the activity for NB hydrogenation was highly affected by the surface area, Co-loading level and Co-Nx coordination in the catalysts. Co@NCG-800 pyrolyzed at 800 °C with 10% Co in the precursor had extraordinary activity for NB hydrogenation, achieving full conversion and 99% aniline selectivity in isopropanol at 100 °C and 1 MPa H2 pressure for 2.5 h. NB conversion and aniline selectivity over the catalysts remained almost unchanged after six recycles, due to the strong coordination between the N- and Co-species. The reaction system showed not only a high NB activity but also a green and durable catalytic process, with easy operation, easy separation and catalyst reusability.

Precapture of CO2 and Hydrogenation into Methanol on Heterogenized Ruthenium and Amine-Rich Catalytic Systems.

A heterogenized alternative to the homogeneous precapture of CO2 with amines and subsequent hydrogenation to MeOH was developed using aminated silica and a Ru-MACHOTM catalyst. Commercial mesoporous silica was modified with three different amino-silane monomers and used as support for the Ru catalyst. These composites were studied by TEM and solid-state NMR spectroscopy before and after the catalytic reaction. These catalytic reactions were conducted at 155 °C at a H2 and CO2 pressures of 75 and 2 bar, respectively, with the heterogeneous system (gas-solid) being probed with gas-phase infrared spectroscopy used to quantify the resulting products. High turnover number (TON) values were observed for the samples aminated with secondary amines.

Mild catalytic transfer hydrogenolysis of lignin for efficient monophenol production over lignin-coordinated N-doped ultrafine Ni nanocluster catalyst

Lignin hydrogenolysis into monophenols presents a promising route for lignin-based chemical and fuel production but still suffers from harsh reaction conditions (e.g. high temperature and high external H2 pressure). Herein, we report an ultrafine Ni nanocluster anchored on N-doped carbon nanosheets (Ni/LNC) for efficient catalytic transfer hydrogenolysis of poplar organosolv lignin. The catalyst was fabricated through a simple pyrolysis process of lignin‑nickel complex mixed with melamine, in which the lignin coordination greatly improved the Ni dispersion and the strong NiN interaction inhibited the Ni nanocluster growth, resulting in the ultrafine particle size (1–2 nm). Under mild conditions (160 °C, 1 h), 22.08% of monophenol yield was obtained over the catalyst, which was significantly higher than those over the two reference catalysts (Ni/AC and Ni/LC) as well as other previously reported Ni-based catalysts. The excellent catalytic activity can be attributed to both the substantial increase in catalytic active sites and the enhancement in H transfer from methanol resulted from the electron-rich N-doped nanosheet support. Finally, magnetically recycled Ni/LNC showed excellent recycling stability. Consequently, this work presents a facile and low-cost approach for the synthesis of N-doped carbon nanosheet supported ultrafine Ni nanocluster and further demonstrates its superior applicability in lignin hydrogenolysis.

Hydrocracking of surgical face masks over Y Zeolites: Catalyst development, process design and life cycle assessment

This study highlights the hydrocracking route for the management of surgical face masks, made of polypropylene, into liquid fuels. Hydrocracking experiments were performed at 325 ℃ and 10 bar cold H2 pressure over Ni-loaded HY and steamed HY zeolites. Ni-loaded steamed Y zeolite demonstrated to be the best catalyst leading to considerably high conversion (100 wt%) and selectivity to liquids (85.5 wt%). The increase in the external surface area and mesoporous volume that improved the bulk polymer molecules diffusion, combined with the uniformly dispersed Ni particles and the additionally generated Lewis acidity, were at the origin of the observed behaviour. This catalyst also showed reasonable stability and ability to be thermally regenerated. From the environmental perspective, life cycle assessment shows the benefits of hydrocracking over pyrolysis and incineration.Therefore, our results demonstrate that Ni-loaded steamed Y zeolites could be promising catalysts for the upcycling of surgical face masks to gasoline range fuels, with minimum environmental impacts.

Active Site Identification for Glycerol Hydrodeoxygenation over the Oxygen Modified Molybdenum Carbide Surface

Density functional theory and microkinetic reactor modeling were used to investigate the hydrodeoxygenation (HDO) mechanism of glycerol on the oxygenated Mo2C catalyst surface to understand the activity and product selectivity under practically relevant reaction conditions. Reactor simulations with multiple active site models predicted that a fully oxygenated surface with acid–base (OH,O) pairs is active for glycerol dehydration and it can selectively cleave one C–O bond to produce 3-hydroxypropanal (HPA). The acid sites are not directly involved in the C–O bond scission process; however, surface oxygen vacancy formation is promoted in the presence of acid sites. The rate-limiting C–O bond cleavage process occurs on the exposed Mo sites with a concerted β-hydrogen transfer to the nearest conjugate base (Mo–O) via an E2 elimination mechanism. Dehydration of HPA to acrolein was observed at longer residence times. Our analysis revealed that reaction conditions, such as temperature and partial pressure of H2, can be tuned to promote further deoxygenation of HPA and acrolein to produce propanal and propylene.

Bifunctional metal-loaded micro-mesoporous zeolites for waste plastics conversion to high quality liquid product

A series of micro-mesoporous zeolitic catalysts synthesized using recrystallization of two different zeolites (HZSM-5 and beta) were impregnated with Pt and other notable metals. The resulting bifunctional catalysts were characterized and tested for the hydrocracking of a model municipal waste plastic mixture. Actual waste plastic mixture of the same composition was also employed for the comparison. The hydrocracking experiments were carried out in a Parr stirred batch reactor at 325, 350, and 375 °C. The other reaction conditions were fixed at the initial cold H2 pressure of 20 bar, reaction time of 60 min, and plastic to catalyst ratio of 20:1 by wt. The inclusion of the Pt metal has shown to increase the hydrocracking activity of the micro-mesoporous supports. The Pt micro-mesoporous ZSM-5 catalysts have shown the better activity while Pt micro-mesoporous beta catalysts have shown better selectivity towards liquid. The presence of Pt metal has also produced a better quality liquid product with fewer unsaturated hydrocarbons and results in lower coke formation as determined by the TGA analysis of the spent catalysts.

Selective Hydrogenation of Phenolic Compounds to Cyclohexanols over Nanosheet Ni@Al2O3 Catalysts

Herein, a series of nanosheet Ni@Al2O3 catalysts were prepared using the one-pot method, which offers good catalytic activity and selectivity of the phenolic compounds in aqueous due to their unique structures with rich active sites and large specific surface areas. The effects of calcination temperature, nickel loading, reaction temperature, and H2 pressure on the catalyst’s performance were studied on the simulated phenolic wastewater. The results indicated that phenolic compounds were selectively converted to the corresponding cyclohexanols regardless of the conversion by the 20%Ni@Al2O3-500 catalyst under mild conditions. Based on the procedure, cyclohexanol and water separation were simulated with the Aspen Plus model. This work provides an alternative scheme for treating phenolic wastewater.

PET Waste Recycling into BTX Fraction Using In Situ Obtained Nickel Phosphide.

The annual production of plastic waste is a serious ecological problem as it causes substantial pollution of the environment. Polyethylene terephthalate, a material usually found in disposable plastic bottles, is one of the most popular material used for packaging in the world. In this paper, it is proposed to recycle polyethylene terephthalate waste bottles into benzene-toluene-xylene fraction using a heterogeneous nickel phosphide catalyst formed in situ during the polyethylene terephthalate recycling process. The catalyst obtained was characterized using powder X-ray diffraction, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy techniques. The catalyst was shown to contain a Ni2P phase. Its activity was studied in a temperature range of 250-400 °C and a H2 pressure range of 5-9 MPa. The highest selectivity for benzene-toluene-xylene fraction was 93% at quantitative conversion.

Influence of Natural Mordenite Activation Mode on Its Efficiency as Support of Nickel Catalysts for Biodiesel Upgrading to Renewable Diesel.

In the present work, natural mordenite originated from volcanic soils in Greek islands, activated using HCl solution and HCl solution followed by NaOH solution, was used as support for preparing two metallic nickel catalysts (30 wt.% Ni). The catalysts were thoroughly characterized (XRF, N2 adsorption-desorption, SEM, XRD, TEM, H2-TPR, NH3-TPD) and evaluated for biodiesel upgrading to green (renewable) diesel. Double activation of natural mordenite optimized its supporting characteristics, finally resulting in a supported nickel catalyst with (i) enhanced specific surface area (124 m2 g-1) and enhanced mean pore diameter (14 nm) facilitating mass transfer; (ii) easier nickel phase reduction; (iii) enhanced Ni0 dispersion and thus high active surface; (iv) balanced population of moderate and strong acid sites; (v) resistance to sintering; and (vi) low coke formation. Over the corresponding catalyst, the production of a liquid consisting of 94 wt.% renewable diesel was achieved, after 9 h of reaction at 350 °C and 40 bar H2 pressure, in a semi-batch reactor under solvent-free conditions.

Branched-chain biofuels derived from hydroisomerization of palm olein using Ni/modified beta zeolite catalysts for biojet fuel production

To overcome mass transfer limitation and adjust zeolite's acidity, the modification of beta zeolite via etching with hydrofluoric acid/ammonium fluoride (HF/NH4F) solution was revealed and the modified beta zeolite was then applied as a support of nickel (Ni) catalysts used for hydroisomerization of palm olein. HF/NH4F solution containing 0.25 M HF concentration was appropriate to enlarge original existing intercrystalline mesopores of beta zeolite (beta-0.25), which resulted to the higher pore volume. The Ni/beta-0.25 catalyst also exhibited the better Ni dispersion and lower acidity. These features suppressed overcracking and provided 43.4 wt% bio-jet fuel yield with 22.1 wt% iso-alkanes fraction when hydroisomerization was operated under 40 bar initial hydrogen (H2) pressure at 340 °C for 5 h. At 0.75 M HF concentration, the excessive leaching of aluminum species out of the zeolite framework provided beta-0.75 with very low acidity, which was ineffective to convert molecules of palm olein to bio-jet fuel range. Initial H2 pressure at 40 bar was sufficient to activate the hydroisomerization of palm olein over Ni/beta-0.25 catalyst to produce liquid biofuel containing iso−/n-alkane ratio of 2.61. The liquid biofuel/Jet A-1 blend at 50% (v/v) had freezing point and gross heating value of −58.9 °C and 43.7 MJ/kg, respectively.

Mild hydrogenolysis of lignin model compound and organosolv lignin over non-noble bimetallic Ni–Fe/TiN catalyst

Lignin is one of the most promising feedstocks for renewable aromatics production. Conversion of such feedstock into aromatics can be attained through catalytic hydrogenolysis. In this work, NixFey/TiN bimetallic catalysts were evaluated in the hydrogenolysis of both: (i) benzyl phenyl ether (BPE) as a model compound for lignin and (ii) real organosolv lignin feedstock under low temperature (150 °C) and low H2 pressure (12 bar). All bimetallic catalysts exhibited superior performance over single-component materials and were shown to compose of uniformly/highly dispersed and intimately mixed Ni and Fe nanoparticles. Among bimetallic materials, Ni5Fe2/TiN possesses the highest activity in BPE hydrogenolysis, which is comparable to that of a 5% Pd/C commercial catalyst while showing significantly higher aromatic selectivity. Ni5Fe2/TiN catalyst also outperformed Pd/C in hydrogenolysis of organosolv lignin, shown by its higher oil yield, greater content of phenolic monomers, and lower content of dimers. This material exhibited good stability in BPE conversion with no noticeable deactivation over 5 recycling cycles. XANES analysis suggests the electron transfer from Ni to Fe, which explains the superior activity observed with Ni5Fe2/TiN.

Synthesis of Ru, Ni and Fe supported graphene nanoplatelets catalysts for hydrogenation of glucose into sorbitol

Non-covalent method of graphene nanoplatelets’ functionalization using the pyrene-tagged Ru, Ni and Fe precursors developed in this work offers an easy way to prepare bimetallic catalysts with different metal ratio and different compositions as Ni-Ru, Fe-Ru and Ni-Fe. First, four different metallic precursors were synthetized: Ni (0), Ni (II), Fe and Ru. Then, 16 different catalysts were prepared and fully characterized by ICP, XPS, XRD and TEM. All catalysts were then tested in the catalytic reaction of the hydrogenation of glucose into sorbitol. The ruthenium supported catalyst with 2.23 wt% shows a good conversion (66%) of glucose and high sorbitol selectivity (74%) at 160 °C under 30 bar H2 pressure during 2 h. The non-noble metallic catalysts Ni and Fe show very low conversion and selectivity. However, the combination of these two metals shows good results: 58% of glucose conversion and 40% of sorbitol selectivity obtained with 4.12 wt% in both metals.

Upcycling waste polycarbonate plastics into jet fuels over NiCo/C by catalytic tandem hydropyrolysis/hydrodeoxygenation

Chemical upcycling of waste polycarbonate (PC) into jet fuels through catalytic tandem hydropyrolysis/hydrodeoxygenation (THH) is a practical strategy to generate value from polymer wastes. A process which combining hydropyrolysis with vapor phase hydrodeoxygenation (HDO) was proposed in a two-stage pressurized fixed-bed reactor. A cobalt-based Metal-Organic Framework (MOF) derived material supported with nickel was designed for the vapor-phase HDO of phenolic compounds derived from PC hydropyrolysis. The product distribution could be regulated by optimizing reaction pressure in the reactor and catalyst to PC mass ratio. Experimental results showed that the products are all phenolic compounds in the absence of catalysts, while a high yield of jet-fuel range cycloalkanes (100%) was obtained under optimized conditions (7 bar H2 pressure and 5:1 catalyst to PC mass ratio) over NiCo/C. The high HDO activity of NiCo/C depends on the synergistic effect of nickel and cobalt atoms, which facilitates the elimination of phenolic hydroxyl group and hydrogenation of benzene ring. This work puts forward an efficient approach for upcycling PC waste into jet fuels with MOF-derived NiCo/C as a catalyst.

Efficient synthesis of sugar alcohols using a composite trimetallic Pt–Ni–Sn/MWCNTs catalyst based on metal element coordination and valence regulation

Functional sugar alcohols are a kind of burgeoning food additives to substitute saccharose due to the prominent biofunctions including moderate sweetness, low calorific values and no influence on blood sugar fluctuation, thus applied widely in food, medical, health protection as well as chemical production. Traditional synthesis of functional sugar alcohols required high temperature and H2 pressure, as well as leading to low reaction efficiency, side reactions and leaching of toxic metal ions. In the present work, Pt–Ni–Sn/MWCNTs catalyst was obtained using a liquid phase reduction method with the transition metals loading of Pt 3.4%, Ni 0.7%, Sn 0.4%, respectively. The catalyst catalyzed the preparation of xylitol, sorbitol, mannitol and galactitol with the high monosaccharide conversion (>99.5%) and yield (>99.1%) under relatively mild conditions (100 °C, 3.0 MPa H2), which were lower than ever reported. For the 13-batch reuse of Pt–Ni–Sn/MWCNTs, the total conversion of xylose was 99.4% and the total yield of xylitol was 99.2%, the productivity of 103.2 g xylitol per gram of catalyst was also obtained. Besides, no side reactions, no metal ions as well as no changes of pH were observed in the reaction process. Our trimetallic catalyst exhibited valuable potential in functional sugar alcohols production.

Copper nanoparticles encapsulated in a nanoporous carbon-based catalyst in the upgradation of γ-valerolactone to 1,4-pentanediol by selective hydrogenation

This research work introduces highly dispersed Cu nanoparticles encapsulated into a nanoporous carbon (Cu@C) structure as an efficient catalytic system in selective hydrogenation of γ-valerolactone (GVL) to 1,4-pentanediol. The nanoporous carbon support and the catalysts were synthesized by sequential novel methods and characterized extensively by using a combination of different analytical techniques to determine the phase, textural, morphology, nanoparticles size, and distribution analysis, and redox behavior. The designed Cu@C embedded catalysts show moderately high activity in GVL hydrogenation with different Cu loadings. The effect of copper loadings was found to be a significant parameter in gaining the best performance in GVL conversion. The copper nanoparticles were uniformly distributed over the nano-scaled carbon structure with active metallic Cu(111) sites with high dispersion and promote GVL hydrogenation, efficiently. Over a 5Cu@C catalyst exhibited the highest GVL conversion (∼91%) and 1,4-pentanediol selectivity (∼97%) at 200 °C for a 5 h reaction time under a 5 MPa H2 pressure. The dispersion of the active copper phase in combination with a smaller particle size and surface acidity is directly correlated with the catalytic performance activity. The effects of reaction parameters such as the reaction time, temperature, and H2 pressure were systematically investigated. Overall, Cu@C is a promising non-noble metal-based catalytic system for the upgradation of biomass-based platform molecules via selective hydrogenation.

Phenol hydrogenation to cyclohexanol catalysed by palladium supported on CuO/CeO2.

Hydrogenation of phenol to cyclohexanone/cyclohexanol is an important reaction in production of nylon-6, nylon-66 and in petroleum industry. Liquid phase phenol hydrogenation over Pd-CuO/CeO2 was carried out under mild conditions. Palladium impregnated over CuO/CeO2 synthesized by co-precipitation method showed excellent catalytic activity for phenol hydrogenation (99% conversion with 80% cyclohexanol yield) at 90ºC and 10bar H2 pressure in water. Commercial 10%Pd/C showed only 8% phenol conversion under identical conditions. The detailed characterization revealed significant improvement in surface area of ceria after addition of CuO and decrease in crystallite size with creation of defects in CeO2 lattice. XPS analysis showed Pd loading on CuO/CeO2 to cause hydrogen spillover on the surface leading to increase in the oxygen vacancies. The interaction of phenol with catalyst surface studied by detailed FTIR analysis, revealed activation of phenol on oxygen vacancy of ceria as phenoxide ion with perpendicular orientation of aromatic ring on catalyst surface.

Toward a Realistic Surface State of Ru in Aqueous and Gaseous Environments

Identifying the surface species is critical in developing a realistic understanding of supported metal catalysts working in water. To this end, we have characterized the surface species present at a Ru/water interface by employing a hybrid computational approach involving an explicit description of the liquid water and a possible pressure of H2. On the close-packed, most stable Ru(0001) facet, the solvation tends to favor the full dissociation of water into atomic O and H in contrast with the partially dissociated water layer reported for ultra-high-vacuum conditions. The solvation stabilization was found to reach -0.279 J m2, which results in stable O and H species on Ru(0001) in the presence of liquid water even at room temperature. Conversely, introducing even a small H2 pressure (10-2 bar) results in a monolayer of chemisorbed H at the interface, a general trend found on the three most exposed facets of Ru nanoparticles. While hydroxyls were often hypothesized as possible surface species at the Ru/water interface, this computational study clearly demonstrates that they are not stabilized by liquid water and are not found under realistic reductive catalytic conditions.

Kinetic Investigation on Selective CO<sub>2 </sub>Hydrogenation to Formic Acid over Rhodium Hydrotalcite (Rh-HT) Catalyst

Abstract—A heterogeneous catalyst, rhodium hydrotalcite (Rh-HT), was synthesized, characterized, and explored for kinetic studies for the hydrogenation of CO2 to formic acid using molecular hydrogen in an autoclave. The catalyst was efficient for the selective formation of formic acid at a moderate temperature with up to 5 catalytic cycles without any significant loss in catalytic activity. The detailed kinetic investigations were performed by determining the rate of formic acid formation as a function of time, catalyst amount, total pressure, partial pressure of CO2, partial pressure of H2, reaction volume, v/v ratio of the mixed solvent of methanol and water, agitation speed, and temperature in a wide range of variation. The rates were found to be dependent on all these parameters. The formic acid formation rate followed the first-order kinetics with respect to the partial pressures of CO2 and H2, and catalyst amount. The best reaction conditions obtained from the kinetic parametric optimisation were, 50 bar total pressure (1/1 p/p, CO2 and H2); 60°C temperature; a mixture of methanol:water solvent (5/1 v/v, 60 mL); 24 h time; and 500 rpm agitation speed to get a TON of 15840 for formic acid with no additional base. The thermodynamic performance of the heterogeneous catalyst Rh-HT was appreciably associated with highly negative entropy. The performance of the catalyst was effectively enhanced by the mixture of water and methanol as a solvent. The mechanistic routes for CO2 hydrogenation to formic acid are proposed and discussed based on the kinetic and experimental observations involving the role of the molecular effect of water used in the solvent.

Changes in structural parameters of SARA fractions during heavy oil hydrocracking using dispersed catalysts

Most of the characterization of SARA fractions of heavy crude oils during hydrocracking reactions is focused only on asphaltenes, and scarce works are devoted to analyze the differences in the structural parameters of all SARA fractions. In this work, a heavy crude oil is upgraded by non-catalytic and catalytic hydrocracking in a batch reactor at low severity conditions (3.9 MPa H2 pressure, 380 °C temperature, 800 rpm stirring rate, and 4 h reaction time). Three ore catalysts (hematite, magnetite and molybdenite) and one analytical grade catalyst (iron oxide) are employed. After reaction, the upgraded oils are first distilled and then separated into SARA fractions by the ASTM D86-16a and ASTM D2007-11 methods, respectively. NMR (1H and 13C), FTIR and GPC analyses are used to characterize SARA fractions before and after hydrocracking. The hydrocracking products exhibited a reduction in the average molecular weight of all SARA fractions as function of the hydrogenation capacity of each catalyst in the following order: Fe2O3 (analytical grade) > Molybdenite > Hematite > Magnetite. The structural parameters of saturates fraction remains unchanged except for the production of small length aliphatic chains from heavier fractions. For aromatics, resins and asphaltenes fractions, the number of aliphatic carbons is reduced due to dealkylation reactions increasing their aromaticity. For resins and asphaltenes fractions, hydrogenation and ring opening reactions are also carried out. Mo-based catalyst is mainly aimed at the conversion of asphaltenes, while the Fe-based catalysts focused on the conversion of resins.