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This review provides an overview of catalytic hydroconversion processes including hydrocracking, hydrogenolysis and hydrodeoxygenation for upcycling of plastic wastes into fuels and valuable chemicals.

Platinum clusters anchored on carbon nanoribbons by vacancy engineering and oxygen functionality for propane dehydrogenation.

Plastics waste has become a major environmental threat, with polyethylene being one of the most produced and hardest to recycle plastics. Hydrogenolysis is potentially the most viable catalytic technology for recycling. Ruthenium (Ru) is one of the most active hydrogenolysis catalysts but yields too much methane. Here we introduce ruthenium supported on tungstated zirconia (Ru-WZr) for hydrogenolysis of low-density polyethylene (LDPE). We show that the Ru-WZr catalysts suppress methane formation and produce a product distribution in the diesel and wax/lubricant base-oil range unattainable by Ru-Zr and other Ru-supported catalysts. Importantly, the enhanced performance is showcased for real-world, single-use LDPE consumables. Reactivity studies combined with characterization and density functional theory calculations reveal that highly dispersed (WO x )n clusters store H as surface hydroxyls by spillover. We correlate this hydrogen storage mechanism with hydrogenation and desorption of long alkyl intermediates that would otherwise undergo further C-C scission to produce methane.

Despite progress in the depolymerization of lignin, only a few studies convert the obtained monomers to value-added products. Here we introduce a strategy to synthesize branched benzene lubricant (BBL) and branched cyclic lubricant (BCL) base oils from lignin-derived monomers and aldehyde. We perform carbon–carbon coupling via Bronsted acid-catalyzed hydroxyalkylation/alkylation (HAA) then hydrodeoxygenation (HDO). Optimum HAA reaction conditions achieve up to 90% guaiacol conversion and an HAA product containing 76% BBL and 24% enal condensation product over a P-SiO2 catalyst. Subsequent HDO of HAA products over an Ir-ReOx/SiO2 catalyst produces a lubricant-ranged mixture of BCL (C24) up to yield (82%) and small fractions of dodecyl cyclohexane and C10 and C15 carbons alkanes. The kinematic viscosity, viscosity index, and Noack volatility of these base oils are comparable to commercial petroleum-derived poly α-olefin Group IV and refrigerant base oils. This approach provides a sustainable pathway for replacing petroleum-derived base oils.

Catalytic non-oxidative dehydrogenation of light alkanes is one of the most promising routes for the production of value-added olefins because of high selectivity to the target alkenes and increased supply of natural and shale gas. In this review, we emphasize the recent advances in the development of metal-based catalysts for the direct dehydrogenation of light alkanes to olefins. Metal-based catalysts including Pt-, Pd-, Rh- and Ni-based catalysts, particularly Pt-based bimetallic catalysts, are summarized and exemplified. A detailed discussion of the structure–performance correlations of these catalysts is presented. We systematically discussed the geometric and electronic effects of the promoters on these metal-based catalysts. Moreover, we highlighted recent advanced strategies for improving the dehydrogenation performance and the stability of metal-based catalysts. In light of the existing contributions, a perspective was provided to evaluate some of the potential avenues into future research. We hope that this review will inspire the rational design of metal-based catalysts to realize efficient direct dehydrogenation of light alkanes for olefins production.

About 97% of lubricant base oils are currently sourced from petroleum and the majority of the rest is produced from vegetable oils. We demonstrate a promising catalytic route to produce base oils from lignocellulosic biomass-derived 2-alkylfurans and ketones via carbon–carbon coupling in neat conditions. Among several homogeneous and heterogeneous acid catalysts tested, a perfluorinated sulfonic acid (Aquivion PW79S) exhibits the best catalytic performance and yields up to 90% renewable furan-containing base oils with the use of a thiol promotor. The effects of the acid strength of the catalysts, molecular size and structure of thiols and ketones, and fraction of thiols are studied. Electronic structure calculations elucidate the reaction pathway and indicate that the thiol reduces the barrier of the rate-determining dehydration step. The structure and properties of base oils can be tuned by using different synthons. These base oils have excellent properties and can be competitive with or surpass the commercial synthetic alkylnaphthalene and furan-containing bio-ester base oils.

Supported inverse metal–metal oxide catalysts have received significant research interest owing to their effective hydrodeoxygenation (HDO) activity toward biomass substrates, but the high cost of the reported catalysts poses a challenge for commercialization. We present the synthesis of a series of metal–metal oxide catalysts, Ir–MOx/SiO2 (M = Re, Mo, W, V, or Nb) and M′–MoOx/SiO2 (M = Rh, Ru, Pt, or Pd) and their HDO performance on multifuran (high carbon) substrates to produce renewable jet and diesel fuels and lubricant base oils. A MoOx-modified Ir/SiO2 catalyst with a Mo/Ir ratio of 0.13 (Ir–MoOx/SiO2) exhibits the highest product yield (78–96%) under mild reaction conditions. Controlled experiments using probe substrates reveal that furan ring hydrogenation and C–O hydrogenolysis of saturated and unsaturated furan rings occur in a sequential manner. The carbon atom adjacent to the furan or saturated furan ring of substrates or intermediate compounds undergoes slow C–C bond scission, resulting in a ...

Single-use plastics impose an enormous environmental threat, but their recycling, especially of polyolefins, has been proven challenging. We report a direct method to selectively convert polyolefins to branched, liquid fuels including diesel, jet, and gasoline-range hydrocarbons, with high yield up to 85% over Pt/WO3/ZrO2 and HY zeolite in hydrogen at temperatures as low as 225°C. The process proceeds via tandem catalysis with initial activation of the polymer primarily over Pt, with subsequent cracking over the acid sites of WO3/ZrO2 and HY zeolite, isomerization over WO3/ZrO2 sites, and hydrogenation of olefin intermediates over Pt. The process can be tuned to convert different common plastic wastes, including low- and high-density polyethylene, polypropylene, polystyrene, everyday polyethylene bottles and bags, and composite plastics to desirable fuels and light lubricants.

Lubricants are an essential part of modern society with an over $146 billion market but have significant environmental footprint. Bio-based lubricant base oils can offer performance advantages over existing oils and mitigate environmental challenges. We describe, for the first time, the synthesis of new bio-based base oils with tunable molecular branches and properties in high yields (>80%) from biomass derived 2-alkylfurans with enals via conjugate addition-hydroxylalkylation/alkylation (CA-HAA) and hydrodeoxygenation reactions. Among several liquid and solid sulfonic acid catalysts tested for the CA-HAA condensation, Aquivion PW79S, a perfluorinated sulfonic acid resin, exhibits the best performance. Subsequent hydrodeoxygenation of the condensation products with an Ir-ReOx/SiO2 catalyst gives up to an 88% yield of lubricant ranged branched alkanes with high selectivity and superior properties compared with commercial mineral group III and synthetic poly-α-olefin (PAO) base oils. Importantly, the molecular size and number of branches of the products can be tuned by varying the molecular size of substrates in the CA-HAA step. The as-synthesized base oils possess tunable properties and are promising for a wide range of applications.

High yields of diesel-range alkanes are prepared by hydrodeoxygenation of vegetable oils and waste cooking oils over ReOx -modified Ir/SiO2 catalysts under mild reaction conditions. The catalyst containing a Re/Ir molar ratio of 3 exhibits the best performance, achieving 79-85 wt % yield of diesel-range alkanes at 453 K and 2 MPa H2 . The yield is nearly quantitative for the theoretical possible long-chain alkanes on the basis of weight of the converted oils. The catalyst retains comparable activity upon regeneration through calcination. Control experiments using probe molecules as model substrates suggest that C=C bonds of unsaturated triglycerides and free fatty acids are first hydrogenated to their corresponding saturated intermediates, which are then converted to aldehyde intermediates through hydrogenolysis of acyl C-O bonds and subsequently hydrogenated to fatty alcohols. Finally, long-chain alkanes without any carbon loss are formed by direct hydrogenolysis of the fatty alcohols. Small amounts of alkanes with one carbon fewer are also formed by decarbonylation of the aldehyde intermediates. A synergy between Ir and partially reduced ReOx sites is discussed to elucidate the high activity of Ir-ReOx /SiO2.

Invited for this month′s cover is the group of Basudeb Saha and Dionisios G. Vlachos at the Catalysis Center for Energy Innovation (CCEI), University of Delaware. The image shows the use of renewable aviation fuels produced from C−C coupled biomass platforms. The Full Paper itself is available at 10.1002/cssc.201700863.

Currently, lubricant base oils are derived from petroleum, a nonrenewable feedstock that contributes to greenhouse gas emissions. Bioderived, renewable lubricant base oils can mitigate environmental challenges and offer superior cold flow properties by incorporating branches to the base oil's hydrocarbon backbone with an appropriate synthetic strategy. A strategy was developed to synthesize branched alkanes for lubricant base oil in two steps from 12-tricosanone, obtained from bioderived fatty acids, and furfural, obtained from lignocellulosic biomass. The reaction pathway involves carbon-carbon coupling through aldol condensation followed by hydrodeoxygenation (HDO). Various solvents (non-polar, aprotic and polar, protic) and reaction conditions were screened to achieve a maximum yield of 94.3 % of aldol condensation products, containing the majority of a C

Deoxygenation of sorbitol was carried out over a Pt-modified Ir-ReOx/SiO2 catalyst in biphasic solvent system (n-decane + H2O) without external hydrogen. Good yield of gasoline-ranged products was obtained including C5–C6 alkanes and C2–C6 mono-functionalized compounds such as ketones, alcohols, cyclic ethers and carboxylic acids. The Pt(3 wt%)-Ir-ReOx/SiO2 catalyst showed the best performance in the production of gasoline-ranged products. The maximum yield of gasoline-ranged products was 42%. The distribution of the products can be tuned by the addition of HZSM-5. The main products were C5–C6 alkanes with addition of HZSM-5 while the main products were C2–C6 mono-functionalized compounds without addition of HZSM-5. Characterizations such as TPR, XRD, TEM, XANES, EXAFS, CO adsorption were performed. The results demonstrated that the Pt-Ir-ReOx/SiO2 catalyst showed the structure of Pt-Ir alloy particles partially covered with ReOx species. The number of surface Pt atoms in Pt(3)-Ir-ReOx/SiO2 was larger than that of Pt/SiO2 or Pt-ReOx/SiO2 because of the small size of Pt-Ir alloy particles. The large number of surface Pt atoms and the synergetic effect of Pt, Ir and ReOx species make the catalyst efficiently generate hydrogen by aqueous phase reforming of sorbitol, and the generated hydrogen is consumed in the hydrogenolysis C O bonds.

Three classes of renewable lubricant base oils with tunable properties were synthesized from biomass or natural oils., We present a strategy to synthesize three types of renewable lubricant base oils with up to 90% yield using 2-alkylfurans, derived from nonfood biomass, and aldehydes, produced from natural oils or biomass through three chemistries: hydroxyalkylation/alkylation (HAA), HAA followed by hydrogenation, and HAA followed by hydrodeoxygenation. These molecules consist of (i) furan rings, (ii) saturated furan rings, and (iii) deoxygenated branched alkanes. The structures of these molecules can be tailored in terms of carbon number, branching length, distance between branches, and functional groups. The site-specific, energy-efficient C–C coupling chemistry in oxygenated biomass compounds, unmatched in current refineries, provides tailored structure and tunable properties. Molecular simulation demonstrates the ability to predict properties in agreement with experiments, proving the potential for molecular design.

Hierarchical ZSM-5 with controllable chainlike structure was hydrothermally synthesized with sucrose as template, characterized by XRD, FT-IR, N 2 adsorption, SEM and TEM, and used for methylation of 2-methylnaphthalene. Hierarchical ZSM-5 can be rapidly synthesized, and chainlike morphology is stacked with several submicron crystals. With increasing sucrose amount in the precursor, the chain structure became more obvious, and the surface area and pore volume of mesopores increased. Narrow mesoporous distribution was centered at about 7 nm. It is thought that the formation of mesopores is related to the template role of sucrose. Chainlike hierarchical ZSM-5 exhibited high 2-methylnaphthalene conversion and 2,6-dimethylnaphthalene yield.

n-Pentane, pentanols and xylitol can be separately produced from hemicellulose (xylan) over an Ir–ReOx/SiO2 catalyst combined with acids by simply adjusting the reaction conditions. n-Pentane can be produced by using Ir–ReOx/SiO2 combined with HZSM-5 + H2SO4 in a biphasic solvent system (4 ml n-dodecane + 9.5 ml H2O) with a reaction temperature of 463 K for 24 h. Pentanols can be produced by using Ir–ReOx/SiO2 combined with H2SO4 in a biphasic solvent system (20 ml n-dodecane + 9.5 ml H2O) with a reaction temperature of 413 K for 144 h. Xylitol can be produced by using Ir–ReOx/SiO2 combined with H2SO4 in the aqueous phase with a reaction temperature of 413 K for 12 h. The highest yields of n-pentane, pentanols and xylitol could reach 70%, 32% and 79%, respectively. The reuse of the catalyst was feasible when the catalyst was regenerated by calcination at 773 K for 3 h. The calcination step is for removing the humins which were formed at the hydrolysis + hydrogenation step during conversion of xylan. The humins covered the active site of Ir–ReOx/SiO2 and HZSM-5, and they deactivated Ir–ReOx/SiO2 in C–O hydrogenolysis performance in part. The mineral ions (such as Na+ and K+) in xylan decreased the hydrogenolysis activity of Ir–ReOx/SiO2 significantly since the mineral ions can make the number of hydroxorhenium sites (Re–OH) smaller, which is the active site of Ir–ReOx/SiO2 for C–O hydrogenolysis, by ion exchange. The appropriate amount of H2SO4 addition is very crucial for the production of target products in high yield. The addition of H2SO4 not only neutralized the residual alkali of xylan after being isolated from lignocellulose to make the reaction solution acidic, but also improved the C–O hydrogenolysis activity of Ir–ReOx/SiO2 through increasing the number of hydroxorhenium sites by competitive adsorption on the Re site with mineral ions.

High yields of diesel-range alkanes are prepared by hydrodeoxygenation of vegetable oils and waste cooking oils over ReO

The total hydrodeoxygenation of carbohydrate-derived molecules to alkanes, a key reaction in the production of biofuel, was reviewed from the aspect of catalysis. Noble metals (or Ni) and acid are the main components of the catalysts, and group 6 or 7 metals such as Re are sometimes added as modifiers of the noble metal. The main reaction route is acid-catalyzed dehydration plus metal-catalyzed hydrogenation, and in some systems metal-catalyzed direct CO dissociation is involved. The appropriate active metal, acid strength, and reaction conditions depend strongly on the reactivity of the substrate. Reactions that use Pt or Pd catalysts supported on Nb-based acids or relatively weak acids are suitable for furanic substrates. Carbohydrates themselves and sugar alcohols undergo CC dissociation easily. The systems that use metal-catalyzed direct CO dissociations can give a higher yield of the corresponding alkane from carbohydrates and sugar alcohols.

Hierarchical ZSM-5 zeolites with controllable structure were hydrothermally synthesized through self-assembly of zeolite seeds by the assistance of cetyltrimethylammonium bromide (CTAB) without other organic co-solvent or additive, and characterized by XRD, FT-IR, SEM, TEM and N2 adsorption. The results show that the synthesized samples are of pure MFI structure with high crystallization, and the crystal sizes of hierarchical ZSM-5 are primary nanoparticles. The addition of CTAB can decrease the primary nanoparticle sizes to 10 nm and hinder further aggregation of nanoparticles into zeolite crystal. The BET surface area, total pore volume and external surface area of hierarchical ZSM-5 samples can be tuned by the amount of CTAB. It is thought that the addition of NaOH and CTAB plays an important role in crystallization and self-assembly of zeolite seeds. Compared with ZSM-5 prepared without CTAB, the hierarchical ZSM-5 shows better stability and 2,6-dimethylnaphthalene yield in the methylation of 2-methylnaphthalene with methanol.

Ru-added Ir-ReOx/SiO2 catalysts worked as efficient catalysts for the selective hydrogenolysis of glycerol to 1,3-propanediol and 1-propanol. 0.9 wt% Ru-added Ir-ReOx/SiO2 catalyst demonstrated high activity for the hydrogenolysis of glycerol to 1,3-propanediol with high selectivity comparative to Ir-ReOx/SiO2. In addition, 4.4 wt% Ru-added Ir-ReOx/SiO2 catalyst with H2SO4aq showed high activity for the selective hydrogenolysis of glycerol to 1-propanol, and the yields of 1-propanol and total propanols (1-propanol + 2-propanol) were 71% and 84%, respectively. On the basis of various analyses such as TPR (temperature-programmed reduction), XRD, XAFS and CO adsorption, the structure and reaction mechanism of Ru-added Ir-ReOx/SiO2 catalysts were proposed.

One-pot conversion of cellulose to n-hexane was carried out over the Ir-ReOx/SiO2 (Re/Ir = 2) catalyst combined with HZSM-5 as cocatalyst in a biphasic reaction system (n-dodecane + H2O). The yield of n-hexane reached 83% from ball-milled cellulose and 78% from microcrystalline cellulose. Even using a high weight ratio of cellulose to water (1:1), a 71% yield of n-hexane could be obtained from ball-milled cellulose. The yield of n-hexane was almost maintained during three repeated tests when the catalyst was calcined again. The transformation of cellulose to n-hexane consists of the hydrolysis of cellulose to glucose via water-soluble oligosaccharides, hydrogenation of glucose to sorbitol, and successive hydrogenolysis of sorbitol to n-hexane. The Ir-ReOx/SiO2 catalyst promotes a hydrogenation and hydrogenolysis step. HZSM-5 enhanced the hydrolysis of cellulose in hot water and C–O bond hydrogenolysis activity of the Ir-ReOx/SiO2 catalyst.

One-pot selective conversion of highly concentrated furfural to 1,5-pentanediol (1,5-PeD) was carried out over Rh-added Ir–ReOx/SiO2 catalysts through two-step reaction temperatures. Over the optimized catalyst, Rh(0.66 wt%)–Ir–ReOx/SiO2, the maximum yield of 1,5-PeD was 71.1% from highly concentrated furfural (50 wt%) and 78.2% from diluted furfural (10 wt%). These values were higher than those obtained with Ir–ReOx/SiO2 or Pd–Ir–ReOx/SiO2 catalysts. Rh–Ir–ReOx/SiO2 showed much higher activity in the hydrogenation of furfural to tetrahydrofurfuryl alcohol intermediate in the low temperature step than Ir–ReOx/SiO2, although the hydrogenation activity was lower than that of Pd–Ir–ReOx/SiO2. A long reaction time in the low temperature step is necessary to obtain a good 1,5-PeD yield over Rh–Ir–ReOx/SiO2 in two-step reaction of furfural. The hydrogenolysis activity of Rh–Ir–ReOx/SiO2 for tetrahydrofurfuryl alcohol to 1,5-PeD in the high temperature step was higher than that of Pd–Ir–ReOx/SiO2 and was comparable to that of Ir–ReOx/SiO2. The characterization results of TPR, XRD, XANES, EXAFS, STEM-EDX and FT-IR of adsorbed CO indicated that Rh–Ir–ReOx/SiO2 catalysts showed the structure of Ir–Rh alloy particles partially covered with ReOx species. The hydrogenation activity of Rh–Ir–ReOx/SiO2 for the furan ring was higher than those of the mixture of Rh–Ir/SiO2 and Ir–ReOx/SiO2 or the mixture of Rh–ReOx/SiO2 and Ir–ReOx/SiO2. Both Ir–Rh alloy formation and ReOx modification of alloy particles are essential for the high hydrogenation activity.

One-pot selective conversion of furfural into 1,5-pentanediol (1,5-PeD) was carried out over Pd-added Ir–ReOx/SiO2catalysts through two-step reaction temperatures. The Pd(0.66 wt%)–Ir–ReOx/SiO2catalyst showed the best performance in the production of 1,5-PeD from furfural. The maximum yield of 1,5-PeD was 71.4%. The furfural conversion and yield of 1,5-PeD was almost maintained during four repeated tests when the catalyst was calcined again. The characterization results from TPR, XRD, XANES, EXAFS and FT-IR of adsorbed CO indicated that Pd–Ir–ReOx/SiO2catalysts consisted of ReOx-modified Pd metal particles and ReOx-modified Ir metal particles. The lower-temperature reaction step was very crucial for the total hydrogenation of furfural into a tetrahydrofurfuryl alcohol intermediate, which was converted into 1,5-PeD by hydrogenolysis during the high temperature step over the ReOx-modified Ir metal particles.

Mesoporous carbons (MCs) were directly prepared from direct coal liquefaction residue (CLR) by KOH activation, and used as catalysts for methane decomposition. The results indicated that the prepared MCs were of a narrow pore size distribution centered at about 3.5 nm. The mineral matters in the CLR and their salts formed during KOH activation process served as templates for mesopore formation, through washing off the mineral matters and the salts occupied in the inner space of the carbon. The resultant MCs showed higher and more stable activity in methane decomposition reaction than commercial coal-based activated carbon and carbon black catalysts.

Activated carbons (ACs) are of good potential to be the catalysts for methane decomposition to produce hydrogen without CO and CO2. Coal liquefaction residue (CLR) seems to be a promising precursor for ACs. In this work, several types of ACs were prepared by KOH activation from Shenhua CLR with addition of SiO2 or SBA-15. The catalytic activity and stability for methane decomposition were investigated and compared with commercial coal-based AC and carbon black (BP2000). The results show that the prepared ACs have larger surface area, narrower pore distribution, and higher catalytic activity than those directly prepared by KOH activation, and are superior to the commercial carbons. The increased microporosity resulting from the soluble salts formed by the reaction between the additive and KOH is responsible for the high catalytic activity.

The total hydrodeoxygenation of carbohydrate-derived molecules to alkanes, a key reaction in the production of biofuel, was reviewed from the aspect of catalysis. Noble metals (or Ni) and acid are the main components of the catalysts, and group 6 or 7 metals such as Re are sometimes added as modifiers of the noble metal. The main reaction route is acid-catalyzed dehydration plus metal-catalyzed hydrogenation, and in some systems metal-catalyzed direct CO dissociation is involved. The appropriate active metal, acid strength, and reaction conditions depend strongly on the reactivity of the substrate. Reactions that use Pt or Pd catalysts supported on Nb-based acids or relatively weak acids are suitable for furanic substrates. Carbohydrates themselves and sugar alcohols undergo CC dissociation easily. The systems that use metal-catalyzed direct CO dissociations can give a higher yield of the corresponding alkane from carbohydrates and sugar alcohols.

Hexanols were produced in high yield by conversion of cellulose over Ir-ReOx /SiO2 (molar ratio Re/Ir=2) catalyst in biphasic reaction system (n-decane+H2 O). The cellulose was depolymerized by mechanocatalysis with the aid of H2 SO4 . The influence of solvent amount, reaction temperature and hydrogen pressure was systematically investigated and the highest yield of hexanols reached 60 % under the conditions of n-decane/water ∼2 (v/v), 413 K, 10 MPa H2 for 24 h. Mechanocatalytic depolymerization of cellulose with the aid of H2 SO4 or HCl and the use of sufficient n-decane were very crucial for the production of hexanols. H2 SO4 not only catalyzed cellulose to water-soluble oligosaccharides but also promoted the hydrogenolysis activity of Ir-ReOx /SiO2 catalyst. The role of n-decane was to extract hexanols and to suppress over-hydrogenolysis of hexanols to n-hexane.