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Recyclable PdCu single atom alloys supported on Al2O3 were applied to the selective hydrogenation of crotonaldehyde to elucidate the minimum number of Pd atoms required to facilitate the sustainable transformation of an α,β-unsaturated carbonyl molecule. It was found that, by diluting the Pd content of the alloy, the reaction activity of Cu nanoparticles can be accelerated, enabling more time for the cascade conversion of butanal to butanol. In addition, a significant increase in the conversion rate was observed, compared to bulk Cu/Al2O3 and Pd/Al2O3 catalysts when normalising for Cu and Pd content, respectively. The reaction selectivity over the single atom alloy catalysts was found to be primarily controlled by the Cu host surface, mainly leading to the formation of butanal but at a significantly higher rate than the monometallic Cu catalyst. Low quantities of crotyl alcohol were observed over all Cu-based catalysts but not for the Pd monometallic catalyst, suggesting that it may be a transient species converted immediately to butanol and or isomerized to butanal. These results demonstrate that fine-tuning the dilution of PdCu single atom alloy catalysts can leverage the activity and selectivity enhancement, and lead to cost-effective, sustainable, and atom-efficient alternatives to monometallic catalysts. [ABSTRACT FROM AUTHOR]

γ‐Valerolactone (GVL) is a renewable and versatile platform chemical derived from sustainable carbon feedstocks. The cascade conversion of levulinic acid into GVL requires Brønsted and Lewis acid catalysed reactions. Here, a dual‐catalyst bed configuration is demonstrated that promotes synergy between Brønsted acid sites in sulfated zirconia (SZ) and Lewis acid sites in ZrO2/SBA‐15 for the liquid phase, continuous flow esterification and subsequent catalytic transfer hydrogenation (CTH) of levulinic acid to GVL. A saturated surface sulfate monolayer, possessing a high density of strong Brønsted acid sites, was optimal for levulinic acid esterification to isopropyl levulinate over SZ (>80 % conversion). A conformal ZrO2 bilayer, deposited over a SBA‐15 mesoporous silica and possessing mixed Brønsted:Lewis acidity, catalysed CTH of the levulinate ester and subsequent dealcoholisation/cyclisation to GVL (>60 % selectivity). Maximum stable productivity for the dual‐bed was 2.2 mmolGVL.gcat.h−1 at 150 °C, significantly outperforming either catalyst alone or a physical mixture of both. Flow chemistry is a versatile approach to achieve spatial control over cascade transformations involving distinct catalytically active sites. [ABSTRACT FROM AUTHOR]

BACKGROUND Modern day scientific endeavour strives towards global sustainability through the smart utilisation of renewable resources as base materials for chemicals. Until now, the most common commercial process to produce levulinic acid (a mass‐produced platform chemical) depends on a two‐stage mineral acid‐catalysed reaction, which generates harmful environmental waste. In this work, an environmentally friendly levulinic acid production route using less harmful organic acids assisted by microwave heating from biomass feedstocks is reported for the first time. RESULTS: Using aluminum sulfate as a green Lewis acid catalyst and seven organic acids, levulinic acid was successfully produced from barley straw under microwave heating, with maleic acid giving the highest catalytic conversion. A Response Surface Methodology (RSM) approach was used to rapidly and effectively examine the effect of five reaction variables on the productivity of the levulinic acid. A wide range of different biomass wastes (barley straw, brewery waste, olive cake, spent tea leaves and potato, tomato, and mandarin peels) were subsequently screened to produce the levulinic acid. The highest yield of 86 wt% based on cellulose content from mandarin peel (a value comparable to a lengthier 'non‐green' route) was achieved under the following optimized reaction conditions: 180 °C, 38 min, 2 M maleic acid concentration, 0.1 g Al2(SO4)3 and 1:22 biomass: maleic acid ratio (g mL−1). CONCLUSIONS: The proposed method is a promising new route towards the green, high yield production of levulinic acid from a variety of agricultural and household lignocellulosic biomass wastes, without the need for pre‐treatment. © 2020 The Authors. Journal of Chemical Technology & Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

Hierarchical Cu2O nanospheres with a Pompon Dahlia‐like morphology were prepared by a one‐pot synthesis employing electrostatic self‐assembly. Nanocomposite analogues were also prepared in the presence of reduced graphene oxide (rGO). Photophysical properties of the hierarchical Cu2O nanospheres and Cu2O/rGO nanocomposite were determined, and their photocatalytic applications evaluated for photocatalytic 4‐chlorophenol (4‐CP) degradation and H2 production. Introduction of trace (<1 wt %) rGO improves the apparent quantum efficiency (AQE) at 475 nm of hierarchical Cu2O for H2 production from 2.23 % to 3.35 %, giving an increase of evolution rate from 234 μmol.g−1.h−1 to 352 μmol.g−1.h−1 respectively. The AQE for 4‐CP degradation also increases from 52 % to 59 %, with the removal efficiency reaching 95 % of 10 ppm 4‐CP within 1 h. Superior performance of the hierarchical Cu2O/rGO nanocomposite is attributable to increased visible light absorption, reflected in a greater photocurrent density. Excellent catalyst photostability for >6 h continuous reaction is observed. [ABSTRACT FROM AUTHOR]

The one-pot conversion of xylose into γ-gammavalerolactone in 2-propanol over bifunctional Zr-Al-Beta zeolites, prepared via a post-synthetic route, was optimized in terms of both catalyst synthesis and reaction conditions. In the catalyst preparation, the use of Zr(NO3)4 as zirconium source as well as the tuning of the amount of water used during the impregnation had a strong impact on the activity of the Zr species due to an improved dispersion of Zr species. As for the aluminium to zirconium exchange, an optimal Al/Zr ratio of 0.20 was identified to provide a catalyst with better activity. The modelization of the catalytic system through experimental design methodology allowed to identify the optimal values of the most influential reaction conditions: temperature 190 °C, catalyst loading 15 g L−1, and starting xylose concentration 30.5 g L−1. Under these optimized reaction conditions, Zr-Al-Beta catalyst provides a GVL yield from xylose (ca. 34%) after only 10 h. The catalysts are stable and reusable after thermal regeneration at 550 °C. [ABSTRACT FROM AUTHOR]

Fast pyrolysis bio-oils possess unfavorable physicochemical properties and poor stability, in large part, owing to the presence of carboxylic acids, which hinders their use as biofuels. Catalytic esterification offers an atom- and energy-efficient route to upgrade pyrolysis bio-oils. Propyl sulfonic acid (PrSO3H) silicas are active for carboxylic acid esterification but suffer mass-transport limitations for bulky substrates. The incorporation of macropores (200 nm) enhances the activity of mesoporous SBA-15 architectures (post-functionalized by hydrothermal saline-promoted grafting) for the esterification of linear carboxylic acids, with the magnitude of the turnover frequency (TOF) enhancement increasing with carboxylic acid chain length from 5 % (C3) to 110 % (C12). Macroporous-mesoporous PrSO3H/SBA-15 also provides a two-fold TOF enhancement over its mesoporous analogue for the esterification of a real, thermal fast-pyrolysis bio-oil derived from woodchips. The total acid number was reduced by 57 %, as determined by GC×GC-time-of-flight mass spectrometry (GC×GC-ToFMS), which indicated ester and ether formation accompanying the loss of acid, phenolic, aldehyde, and ketone components. [ABSTRACT FROM AUTHOR]

New insight was gained into the acidity-reactivity relationships of sulfated zirconia (SZ) catalysts prepared via (NH4)2SO4 impregnation of Zr(OH)4 for propanoic acid esterification with methanol. A family of systematically related SZs was characterized by bulk and surface analyses including XRD, XPS, TGA-MS, N2 porosimetry, temperature-programmed propylamine decomposition, and FTIR of adsorbed pyridine, as well as methylbutynol (MBOH) as a reactive probe molecule. Increasing surface sulfation induces a transition from amphoteric character for the parent zirconia and low S loadings <1.7 wt %, evidenced by MBOH conversion to 3-hydroxy-3-methyl-2-butanone, methylbutyne and acetone, with higher S loadings resulting in strong Brønsted-Lewis acid pairs upon completion of the sulfate monolayer, which favored MBOH conversion to prenal. Catalytic activity for propanoic acid esterification directly correlated with acid strength determined from propylamine decomposition, coincident with the formation of Brønsted-Lewis acid pairs identified by MBOH reactive titration. Monodispersed bisulfate species are likely responsible for superacidity at intermediate sulfur loadings. [ABSTRACT FROM AUTHOR]

γ-valerolactone ( GVL) is an important intermediate chemical with a wide range of applications as fuel, fuel additive and as a green solvent which has received a great deal of attentions from both academia and industry. This review aims to summarise the advances in conversion of renewable feedstocks into GVL through heterogeneous catalytic transfer hydrogenation ( CTH) with a strong emphasis on discussing preparation, characterisation and performance of the catalysts in order to provide a better understanding of various catalytic systems and also to compare them in terms of catalytic performance. © 2017 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

The impact of alkyl chain length on the esterification of C2–C16 organic acids with C1–C4 alcohols has been systematically investigated over bulk and SBA-15 supported sulfated zirconias (SZs). Rates of catalytic esterification for methanol with acetic acid are directly proportional to the sulfur content for both SZ and SZ/SBA-15, with the high dispersion of SZ achievable in conformal coatings over mesoporous SBA-15 confering significant rate-enhancements. Esterification over the most active 0.24 mmol gcat−1 bulk SZ and 0.29 mmol gcat−1 SZ/SBA-15 materials was inversely proportional to the alkyl chain length of alcohol and acid reactants; being most sensitive to changes from methanol to ethanol and acetic to hexanoic acids respectively. Kinetic analyses reveal that these alkyl chain dependencies are in excellent accord with the Taft relationship for polar and steric effects in aliphatic systems and the enthalpy of alcohol adsorption, implicating a Langmuir–Hinshelwood mechanism. The first continuous production of methyl propionate over a SZ fixed-bed is also demonstrated. [ABSTRACT FROM AUTHOR]

[Display omitted] • The mechanism of levoglucosan conversion over HZSM-5 was investigated. • Catalytic fast pyrolysis of levoglucosan, furfural and furan were carried out. • Experiments and DFT modelling were employed to elucidate the reaction mechanism. • The mechanism of direct catalytic route from levoglucosan to furan was revealed. In this work, we have investigated the complicated reaction network of biomass catalytic fast pyrolysis, particularly the decomposition of the key cellulose pyrolysis intermediate, levoglucosan. Fast pyrolysis of levoglucosan using a Py-GC-MS-FID system in the presence of HZSM-5 suggested that furan and furfural are key intermediates to aromatic hydrocarbons. This was followed by theoretical modelling adopting density functional theory (DFT) to unravel the details of the catalytic reaction mechanism from levoglucosan to furan. Our investigations revealed for the first time a direct route from levoglucosan to furan without furfural as an intermediate, with the highest energy barrier along the most favourable pathway to be 2.15 eV. Combined with previously reported mechanisms in the literature, we provide here a detailed reaction network for the conversion of cellulose-derived intermediates to aromatic hydrocarbons. [ABSTRACT FROM AUTHOR]

A family of tungstated zirconia solid acid catalysts were synthesised via wet impregnation and subsequent thermochemical processing for the transformation of glucose to 5-hydroxymethylfurfural (HMF). Acid strength increased with tungsten loading and calcination temperature, associated with stabilisation of tetragonal zirconia. High tungsten dispersions of between 2 and 7 W atoms·nm-2 were obtained in all cases, equating to sub-monolayer coverages. Glucose isomerisation and subsequent dehydration via fructose to HMF increased with W loading and calcination temperature up to 600 °C, indicating that glucose conversion to fructose was favoured over weak Lewis acid and/or base sites associated with the zirconia support, while fructose dehydration and HMF formation was favoured over Brönsted acidic WOx clusters. Aqueous phase reforming of steam exploded rice straw hydrolysate and condensate was explored heterogeneously for the first time over a 10 wt% WZ catalyst, resulting in excellent HMF yields as high as 15% under mild reaction conditions. [ABSTRACT FROM AUTHOR]

Here we describe a simple route to creating conformal sulphated zirconia monolayers throughout an SBA-15 architecture that confers efficient acid-catalysed one-pot conversion of glucose to ethyl levulinate [ABSTRACT FROM AUTHOR]

Pyrolysis bio-oils contain significant amounts of carboxylic acids which limit their utility as biofuels. Ketonisation of carboxylic acids within biomass pyrolysis vapours is a potential route to upgrade the energy content and stability of the resulting bio-oil condensate, but requires active, selective and coke-resistant solid acid catalysts. Here we explore the vapour phase ketonisation of acetic acid over Ga-doped HZSM-5. Weak Lewis acid sites were identified as the active species responsible for acetic acid ketonisation to acetone at 350 °C and 400 °C. Turnover frequencies were proportional to Ga loading, reaching ~6 min−1 at 400 °C for 10Ga/HZSM-5. Selectivity to the desired acetone product correlated with the weak:strong acid site ratio, being favoured over weak Lewis acid sites and reaching 30% for 10Ga/HZSM-5. Strong Brønsted acidity promoted competing unselective reactions and carbon laydown. 10Ga/HZSM-5 exhibited good stability for over 5 h on-stream acetic acid ketonisation. [ABSTRACT FROM AUTHOR]

The thermal sintering under oxidative conditions of Rh nanoparticles supported on oxides characterized by very different oxygen storage capacities (OSC) and labilities was studied at 750 and 850 °C. Under sintering conditions, significant particle growth occurred for Rh/γ-Al2O3 (up to 120% at 850 °C). In striking contrast, Rh/ACZ (alumina–ceria–zirconia) and Rh/CZ (ceria–zirconia) exhibited marked resistance to sintering, and even moderate (ca. −10% at 850 °C) to pronounced (ca. −60% at 850 °C) redispersion of the Rh. A model is proposed based on a double-layer description of metal–support interactions assigned to back-spillover of labile oxygen ions onto the Rh particles, accompanied by trapping of atomic Rh by the resulting surface oxygen vacancies. This model accounts for the observed resistance to sintering and actual redispersion of Rh, consistent with both alternative sintering mechanisms, namely Ostwald ripening (OR) or particle migration and coalescence (PMC). [ABSTRACT FROM AUTHOR]