Supplementary Figure S1 Reactor setup Calcined catalyst (.4 g) and silicon carbide powder (.4g) were mixed thoroughly and inserted into a 4 mm diameter silica reactor (G). The powder mixture was sandwiched between silica wool plugs (I). The silica reactor (G) was wound with a thermocouple which connected the reactor to the temperature-programmable furnace (J and F). Before testing, the catalyst was pretreated under a 1% N 2 gas stream at 2 ml/min and a pure H 2 gas stream at 1ml/min from room temperature up to 15 o C for 2.5 hours (sufficient for extensive reduction of Cu from most Cu containing samples without severe metal sintering according to our experience). After the pre-treatment, the testing started with a flow of methanol/water solution (B) at a CH 3 OH: H 2 O ratio of 1:2, delivered from the HPLC pump (D) at a flow rate of.1ml/min. A N 2 gas stream (A) was co-fed simultaneously with the methanol/water solution at a flow rate of 1ml/min, controlled by a mass-flow controller (C and E). All liquids in the methanol, water and nitrogen co-feeds were fully converted into a gas mixture by passing through pre-heated tubing maintained at 15 o C before arriving at the reactor. A pre-weighed two-necked flask was placed in a dry-ice bath (K and L) to remove excess water and methanol from the reacted mixture. After passing through the dry-ice cold trap, the remaining product gas stream reached the precalibrated gas chromatograph with a thermal conductivity detector (M). The quantity of each individual gas in the product, including H 2, CO, CO 2, N 2 and CH 4, could then be determined and analyzed using the computer (O). To ensure an accurate determination of CO level, a separate FID (N) equipped with a methanator with a lower detection limit than the TCD (below 1 ppm) was also used. 1
TCD Signal (mv) H 2 Consumed (mol) 1.5g.1g.15g 2.x1-4 Slope = 5.97E-11 8 1.5x1-4 6 1.x1-4 4 2 5.x1-5 1 2 3 4 5 Time (s).. 5.x1 5 1.x1 6 1.5x1 6 2.x1 6 2.5x1 6 3.x1 6 3.5x1 6 TPR Peak Area Supplementary Figure S2 Calibration plots. Calibration plots of Cu(II) oxide samples for TPR using the following formulae. The Cu dispersion is defined using the formulae in the Supplementary Methods
Temp/C Supplementary Figure S3 Microscopy of Cu catalyst. (a) Bright field imaging of typical CuZnGaOx catalyst showing dark Cu rich particles (upper left); (b) High magnification showing lattice fringes matching with the spinel phase of ZnGa 2 O 4 (upper right); (c) Cu crystalline sizes (nm) derived from XRD of quenched samples after dwelling at designated temperatures (1 h) which show a significant sintering of CuGaOx without Zn 2+ ; (d) HADDF-STEM imaging of Cu particles (7-8nm) and two small copper clusters pointed by white arrows (.5-1 nm). 3
Supplementary Figure S4 XPS spectroscopy. The XPS survey scan confirms the presence of Cu, Zn, Ga and O. The typical peak of Cu 2p 3/2 at 933.6 ev and two characteristic satellite peaks at 941.2 and 943.4 confirm the existence of Cu(II) before the reduction (lower left). However, the reduced sample (no satellite peak) contains typical bulk Cu 2p 3/2 peak of 932.4 ev and also small Cu clusters peak at slightly higher BE of 934.2 ev 13.
Detector (mv) 7 6 5 4 ZnO Ga 2 O 3 ZnGaOx 43% Cu-Zn.6 Ga.4 O x 43% Cu-ZnGaO x 43% Cu-Zn.25 Ga.75 O x HiFUEL 12 Activation Wavelength: 35 nm 3 2 1 2 4 6 8 1 Sample Temperature ( C) 35 4 45 5 55 6 65 Wavelength, nm Supplementary Figure S5 TPR and photoluminescence measurements. (a) TPR profiles for calcined ZnO, Ga 2 O 3 and ZnGaO x (left); (b) photoluminescence of CuZnGaOx at different Zn:Ga ratios (right). 5
Gas Content / % CO Selectivity / % Gas Content / % CO Selectivity / % 8 Gas content after reaction - catalyst: Cu-ZnGaOx 1.5 8 Thermodynamic Equilibrium at the Experimental Condition 1.5 7 6 5 4 Hydrogen Carbon Dioxide CO Selectivity / % 1 7 6 5 4 1582 2231 243 2528 Hydrogen Carbon Dioxide 2585 2622 1 3 2 511.5 3 2 CO Selectivity / %.5 1 143 95 76 63 55 1.2.4.6.8.1.12 Feed Rate / ml min -1.2.4.6.8.1.12 Feed Rate / ml min -1 Supplementary Figure S6 Feed rate dependent catalytic performance. A plot of catalytic performance, gas content & CO selectivity, against liquid feed rate for the direct steam reforming of methanol by (a) CuZnGaO x catalyst; (b) thermodynamic calculations (Reaction conditions:.4 g cat. +.4 g SiC; 195 o C; CH 3 OH: H 2 O = 1: 2; N 2 carrier @ 1 ml/min.; varying liquid feed rate).
Gas Content / % Methanol Conversion / % Gas Content / % Methanol Conversion / % 14 4 5 Thermodynamic Equilibrium at the Experimental Condition 12 1 Hydrogen 3 4 1 8 8 6 Carbon Dioxide Methanol Conversion / % 2 3 2 Hydrogen Carbon Dioxide Methanol Conversion / % 6 4 4 2 1 1 2 1 : 1 1 : 1.2 1 : 1.5 1 : 2 1 : 3 1 : 5 1 : 1 1 : 2 Methanol : Water @ molar ratio 1 : 1. 1 : 1.2 1 : 1.5 1 : 2. 1 : 3. 1 : 5. 1 : 1 1 : 2 Methanol : Water @ Molar Ratio Supplementary Figure S7 Methanol to water ratio dependent catalytic performance. A plot of catalytic performance, gas content & CO selectivity, against methanol: water molar ratio by (a) CuZnGaO x catalyst; (b) thermodynamic calculations (Reaction conditions:.4 g cat. +.4 g SiC; 195 o C; CH 3 OH: H 2 O = 1: 2; N 2 carrier @ 1 ml/min.; varying liquid feed rate). 7
Methanol Conversion / % Hydrogen productivity / ml/min 2 Methanol conversion as a function of contact time 3 Hydrogen productivity as a function of liquid feed rate 16 2.5 12 2 8 4 1.5 1.5 2 4 6 8 1 12 14 16 18 2 W/F [ kg cat. / ( mol. / sec. of methanol) ] 2 4 6 8 1 12 14 16 18 2 W/F [ kg cat. / ( mol. / sec. of methanol) ] Supplementary Figure S8 Contact time dependent catalytic performance. (a) A plot of catalytic performance, gas content & CO selectivity, against contact time with CuZnGaO x catalyst. (Reaction conditions:.4 g cat. +.4 g SiC; 15 o C; CH 3 OH: H 2 O = 1: 2; N 2 carrier @ 1 ml/min.; varying liquid feed rate); (b) a plot of the hydrogen productivity obtained with the reaction condition as presented in Supplementary Figure S8(a).
Supplementary Table S1: Precursors and recipe contents in synthesising typical catalysts Catalyst Formulation Cu(NO 3 ) 2 3H 2 O/g K-25 Zn(NO 3 ) 2 6H2O/g Ga(NO 3 ) 3 9H 2 O/g Composition (atom %) (Cu : Zn : Ga) CuZnO x 3.65 4.932 43 : 57 : K-29 CuZnGaO x 3.313 4.122 1.233 43 : 47 : 1 K-28 CuGaO x 3.36 7.7 43 : : 57 9
Supplementary Methods: Calibration of Cu(II) oxide samples for TPR The specific Cu metal surface area of the catalyst was calculated as: The specific Cu metal surface area of Cu in the catalyst was calculated as: The Cu particle size was calculated as being the average diameter of the Cu particles on the surface, assuming spherical geometry: (NB. The above calculations are valid only by making the assumption that N 2 O is decomposed to N 2, with the simultaneous oxidation of surface Cu to Cu 2 O) The TPR and PL profiles Neither ZnO nor Ga 2 O 3 are reduced in the temperature range studied, but ZnGaO x shows a small but significant reduction peak at ~55 o C (Supplementary Figure S5a), which indicates the more facile reduction of O 2- species within the ZnGaO x structure, which will be accompanied by the formation of oxygen vacancies and small cations reduction (site migration) in this lower band gap semiconducting material. The photoluminescence (PL) spectra with activation wavelength of 35nm (Supplementary Figure S5b) also indicates that the recombination of excitons takes place at higher wavelengths due to the presence of defects, the concentrations of which are highly dependent on the Zn:Ga ratios used. Non-stoichiometric spinels (NSS) containing Cu have been reported in the literature. 2 It was found that spinels containing excess Cu were able to accommodate the extra Cu ions as interstitial Cu + within the spinel lattice. The mechanism for the formation of interstitial Cu + is proposed as occurring via loss of oxygen, as follows: It is envisaged that excess Cu 2+ may also enter the defective spinel phase to fill the vacant lattice sites, forming a non-stoichiometric phase. Cu 2+ (d 9 ) in an O h environment exhibits the Jahn-Teller effect, causing elongation and hence weakening of the Cu-O
bonds along the axial plane. This axial distortion is what drives the formation of the tetragonal spinel phase observed in the case of our CuGa 2 O 4. 21 However, partially substituting Cu 2+ for Zn 2+ (d 1 ) may help to remove the instability caused by the Jahn- Teller effect, therefore stabilising the material in the cubic NSS phase observed for CuZnGaO x. 22 Optimization of H 2 production The contact time study of the methanol/water reaction over the catalyst was carried out by alternating the liquid feed rate. As shown in Supplementary Figure S6, there was a 511 ppm CO contamination in the product gas at 195 o C at a liquid feed rate of.1 ml/min. From there, the reaction temperature was kept identical but the methanol-water feeding rate was varied. Supplementary Figure S6 (a) shows clearly a declining CO content when the liquid feed rate was increased. It is noted that the CO selectivity of the steam reforming of methanol was moving away from its thermodynamic equilibrium value when the catalyst contact time was decreased, as shown in Supplementary Figure S6 (b). This result indicates that CO 2 and H 2 are the primary products but CO is a secondary product probably via the reversed water gas shift (RWGS) reaction which is a slow reaction under these conditions. The use of shorter contact time obviously enables the suppression of CO content with respect to the equilibrium. It is thus clear that the key CO formation could be suppressed or severely reduced either by decreasing the reaction temperature or the contact time, where the slow RWGS reaction is discouraged. Since there was no detectable CO formation at or below 15 o C, the next objective was to promote the methanol conversion while keeping the CO formation at its minimum. Different concentrations of methanol in water liquid feed were therefore employed at a total liquid feed rate of.1 ml/min in N 2 at 1 ml/min over the catalyst at 15 o C. It is important to note that there was no CO detected for all methanol to water ratios at this temperature. Supplementary Figure S7 (a) shows that methanol conversion can reach 36%, giving 3:1 H 2 /CO 2 with the methanol: water molar ratio set at 1: 2. It is useful to measure the hydrogen productivity from this low temperature NSGDSR over the CuZnGaO x catalyst at 15 o C where no detectable CO is evident. The hydrogen productivities were evaluated at different methanol-water liquid feeding rates while keeping the other reaction parameters constant. Supplementary Figure S8(a) shows that there is a linear relationship between contact time and the methanol conversion at 15 o C. Further increase in methanol conversion to give the primary CO 2 /H 2 products is expected at longer contact time without producing the CO gas. Supplementary Figure S8(b) gives the corresponding hydrogen productivities based on the methanol conversions in Supplementary Figure S8(a). It is evident from Supplementary Figure 11
S8(b) that the best hydrogen productivity so far obtained under our testing conditions was 2.624 ml-h 2 /min where the corresponding methanol-water feeding rate was kept at.2 ml/min. This corresponds to a hydrogen productivity of 393.6 ml-h 2 /g cat./hour.
Supplementary References 2. Payer, A.; Schöllhorn, R.; Ritter, C.; Paulus, W. Neutron diffraction study of the structure of chalcogen spinels Cu 1+y Cr 2 X 4 (X Se, Te). Journal of Alloys and Compounds 191, 37-42 (1993). 21. Biswas, S.K.; Sarkar, A.; Pathak, A.; Pramanik, P. Studies on the sensing behaviour of nanocrystalline CuGa 2 O 4 towards hydrogen, liquefied petroleum gas and ammonia. Talanta 81, 167-1612 (21). 22. Guisnet, M. Heterogeneous catalysis and fine chemicals III: proceedings of the 3rd international symposium, Poitiers, April 5-8, 275-282 (1993). 13