Porous Zirconium–Phytic Acid Hybrid: a Highly Efficient Catalyst for Meerwein–Ponndorf–Verley Reductions

Abstract

The utilization of compounds from natural sources to prepare functional materials is of great importance. Herein, we describe for the first time the preparation of organic-inorganic hybrid catalysts by using natural phytic acid as building block. Zirconium phosphonate (Zr-PhyA) was synthesized by reaction of phytic acid and ZrCl4 and was obtained as a mesoporous material with pore sizes centered around 8.5 nm. Zr-PhyA was used to catalyze the mild and selective Meerwein-Ponndorf-Verley (MPV) reduction of various carbonyl compounds, e.g., of levulinic acid and its esters into γ-valerolactone. Further studies indicated that both Zr and phosphate groups contribute significantly to the excellent performance of Zr-PhyA.

Porous, Naturally Derived Hafnium Phytate for the Highly Chemoselective Transfer Hydrogenation of Aldehydes with Other Reducible Moieties

“…In contrast, Zr‐Phy provided a slightly lower conversion of cinnamaldehyde (91.2 %; Table , entry 3) than Hf‐Phy. The higher activity of Hf‐Phy may be caused by the fact that the oxophilicity of Hf is higher than that of Zr because the dissociation enthalpy of a typical Hf−O bond (802 KJ mol −1 ) is higher than that of a Zr−O bond (776 kJ mol −1 ), which is beneficial for activation of the aldehyde group in cinnamaldehyde (a key step for transfer hydrogenation as discussed below). Moreover, commercial HfO 2 showed very low activity with a cinnamaldehyde conversion of only 2.7 % (Table , entry 4).…”

“…The local environments of Hf in Hf‐Phy and HfO 2 were examined by X‐ray photoelectron spectroscopy (XPS). As shown in Figure a, the binding energies of Hf 4d in Hf‐Phy are higher than those in HfO 2 ; this is indicative of a higher positive charge on the Hf atoms in Hf‐Phy, which results in stronger oxophilicity . The stronger oxophilicity of Hf in Hf‐Phy is helpful in activating the aldehyde groups, which is the key step for the CTH of aldehydes with ORMs (Scheme ), and thus, the reaction is improved.…”

“…As examined by CO 2 temperature‐programmed desorption (TPD), Hf‐Phy has higher basicity than HfO 2 (Figure b), which may be caused by the higher basicity of the phosphate groups . Higher basicity favors activation of the hydroxy group in i PrOH by the basic sites (O 2− ) in the phosphate groups with the aid of Hf 4+ (Scheme ), and this effect could enhance the transfer hydrogenation. Third, as examined by XRD, Hf‐Phy is amorphous with very low crystallinity, whereas HfO 2 shows better crystallinity (Figure c).…”

Acid–Base Bifunctional Hf Nanohybrids Enable High Selectivity in the Catalytic Conversion of Ethyl Levulinate to γ-Valerolactone

“…The binding energy intensity of Hf 4f (Lewis acid) in PPOA-Hf shows the positive charge on the Hf atoms, which resulted in a stronger Lewis acidity with a higher Hf ratio [47]. Furthermore, the binding energy of the O element was also studied, where the lower binding energy of O 1s was correlated with a higher negative charge on the O atom, which resulted in stronger Lewis basicity of O [48]. It is not difficult to see that the strength of acidic and basic sites in the PPOA-Hf-x catalysts is negatively correlated with the increase in PPOA/Hf ratio ( Figure 4).…”

Highly Efficient Hydrogenation of Levulinic Acid into γ‐Valerolactone using an Iron Pincer Complex

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Introduction

The depletion of fossil fuels with increasing emission of carbon dioxide has led to the search for alternative sustainable energy and chemicals sources such as biomass. [3][4][5][6][7] Compared to heterogeneous catalysts, [3,4] homogeneous catalysts have high catalytic efficiency towards hydrogenation of LA or levulinate esters and turnover numbers( TONs) of approximately 174 000 have been achieved (Scheme 1). [2] In the presence of ah eterogeneous or homogeneous metal catalysts, levulinic acid (LA), whichi sp roduced by acid-catalyzed hydrolysis of cellulose to glucosef ollowed by in situ isomerization (to form fructose), dehydration( to form 5-HMF), andd eformylation in a biorefinery process, [1] can be converted into GVL through hydrogenation and dehydrative ring closure.

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