xNi–yCu–ZrO₂ catalysts for the hydrogenation of levulinic acid to gamma valorlactone

Figures & data

Figure 1. Catalytic activity of xNi–yCu–ZrO₂ catalysts prepared with different compositions and reduction temperatures. Reaction conditions: 200 °C, 35 bar H₂, 30 min, 5 wt.% LA/H₂O, catalyst (0.05 g).

Figure 2. Time-on-line data for xNi–yCu–ZrO₂ prepared with different Ni–Cu compositions reduced at 400 °C. Reaction conditions: 200 °C, 35 bar H₂, 5 wt.% LA/H₂O, catalyst (0.05 g) ●: 50Cu–ZrO₂ (pre-reduced at 300 °C); ■: 5Ni–45Cu–ZrO₂; ▲: 15Ni–35Cu–ZrO₂; Δ: 35Ni–15Cu–ZrO₂; □: 45Ni–5Cu–ZrO₂; ○: 50Ni–ZrO₂.

Table 1. Initial rates and TONs for Cu–ZrO₂, Ni–ZrO₂, and xNi–yCu–ZrO₂ catalysts.

Catalyst	Initial rate of reaction/mol dm^−3 s^−1	TON at 30 min/gGVL gcat^−1
50Cu–ZrO2	8.26 × 10^−5	1.71 × 10^−3
5Ni–45Cu–ZrO2	6.43 × 10^−5	1.14 × 10^−3
15Ni–35Cu–ZrO2	6.43 × 10^−5	1.14 × 10^−3
35Ni–15Cu–ZrO2	1.21 × 10^−4	2.31 × 10^−3
45Ni–5Cu–ZrO2	1.32 × 10^−4	2.70 × 10^−3
50Ni–ZrO2	5.56 × 10^−5	1.06 × 10^−3

Notes: Reaction conditions: 200 °C, 35 bar H₂, 30 min, 5 wt.% LA/H₂O, catalyst (0.05 g). Linear fits for initial rates are shown in figure S1. All samples pre-reduced at 400 °C, except 50Cu–ZrO₂ (pre-reduced at 300 °C).

Figure 3. Dependency of GVL yield on reagent concentrations for determining reaction order for (a) LA, and (b) H₂. Reaction conditions: in both cases 200 °C, 30 min reaction, 45Ni–5Cu–ZrO₂ reduced at 400 °C (0.05 g). For (a) 35 bar H₂, and for (b) 5 wt.% LA/H₂O.

Figure 4. XRD patterns of xNi–yCu–ZrO₂ catalysts, reduced at 400 °C and 50Cu–ZrO₂ reduced at 300 °C. (a): Full diffraction pattern; (b): diffraction pattern zoomed to show 2θ = 42–46° traces are aligned with the material of the same composition in (a). Reflections due to known phases are marked as: ●: ZrO₂; ▲: NiO; ■: Ni; ▼: Cu; ♦: Cu–Ni.

Table 2. Physical properties of materials xCu-yNi–ZrO₂.

Catalyst	Alloy particle size^a/nm	BET surface area^b/m^2 g^−1	Specific adsorption of N2O^c/μL g^−1
50Cu–ZrO2	–	60	580
5Ni–45Cu–ZrO2	20	50	670
15Ni–35Cu–ZrO2	15	65	1440
35Ni–15Cu–ZrO2	9	90	1580
45Ni–5Cu–ZrO2	7	110	3160
50Ni–ZrO2	–	80	380

^a Average particle sizes of the Ni–Cu alloy species calculated using the Scherrer equation at 2θ = 42–46°.

^b BET surface area.

^c N₂O adsorption data of catalysts prepared with different Cu–Ni content.

Figure 5. TPR profiles of xNi–yCu–ZrO₂ catalysts, compositions as indicated for each trace.

Table 3. XPS analysis of xNi–yCu–ZrO₂ catalysts.

Catalyst	Binding energies/eV
	Ni (2p3/2)	Cu (2p3/2)
50Cu–ZrO2	–	932.9
5Ni–45Cu–ZrO2	855.5	932.6
15Ni–35Cu–ZrO2	855.8	932.3
35Ni–15Cu–ZrO2	855.6	932.4
45Ni–5Cu–ZrO2	855.3	932.1
50Ni–ZrO2	854.9	–

Figure 6. DOS plots for bulk Ni (solid line), Ru (dashed line), and Cu (dot-dash line). Calculated d-band centres (in eV) are shown as dotted vertical lines labelled by metal type. Spin up states are shown as positive and spin down negative DOS values.

Figure 7. Calculated d-band centre as a function of Ni mole fraction in a 2 × 1 supercell of bulk Cu. Spin up (dotted line) and spin down (solid line) contributions are plotted separately, asymmetry between d-band centres becomes more pronounced as the mole fraction of Ni is increased.

Figure 8. XRD patterns of 45Ni–5Cu–ZrO₂ before and after reaction. ●: ZrO₂; ▲: NiO; ■: Ni; ▼: Cu; ♦: Cu–Ni.

Table 4. Metal leaching from the xNi–yCu–ZrO₂ catalyst in the post-reaction solution obtained by MP-AES.

Sample	Cu leaching/ppm	Ni leaching/ppm
50Cu–ZrO2	0.2	n/a
5Ni–45Cu–ZrO2	0.3	25.2
15Ni–35Cu–ZrO2	0.2	36.4
35Ni–15Cu–ZrO2	1.5	24.9
45Ni–5Cu–ZrO2	0.2	42.9
50Ni–ZrO2	n/a	39.4

Figure 9. The effect of leached metal on GVL yield. ●: 45Ni–5Cu–ZrO₂ catalyst present (0.05g); ○: 45Ni–5Cu–ZrO₂ removed after 30 min. Reaction conditions: 200 °C, 35 bar H₂, 5 wt.% LA/H₂O.

Table 5. Metal leaching from 45Ni–5Cu–ZrO₂ after reaction with various substrates.

Substrate	Cu leaching/ppm	Ni leaching/ppm
Levulinic acid	0.2	42.9
GVL	0.0	9.7
Pentanoic acid	0.2	16.2
2-Pentanone	0.1	3.0