Role of Re and Ru in Re Ru/C Bimetallic Catalysts for the Aqueous Hydrogenation of Succinic Acid Xin Di a, Chuang Li a, Bingsen Zhang b, Ji Qi a, Wenzhen Li c, Dangsheng Su b, Changhai Liang a, * a Laboratory of Advanced Materials and Catalytic Engineering, School of Chemical Engineering, Dalian University of Technology, Dalian 116024, P. R. China. b Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, P. R. China c DCBE, Biorenewables Research Laboratory, Iowa State University, Iowa 50011, United States. * Corresponding author: Tel/Fax: +86 411 84986353; E-mail address: changhai@dlut.edu.cn. 1
1. Catalysts Preparation The scheme of microwave-assistant thermolytic method Scheme S1. The preparation process of Re-Ru catalysts with microwave-assistant thermolytic method. 2. Characterization Method The actual loading of Re and Ru in bimetallic catalysts were analyzed by inductively coupled plasma atomic emission spectroscopy equipment (ICP-AES, Optima 2000DV, PerkinElmer, USA) after dissolution of the catalysts. CO chemisorption was measured with Autosorb-iQ (Quantachrome, USA) equipment to estimate metal dispersion of the Re-Ru/C bimetallic catalysts. Prior to CO chemisorption, the samples were reduced in situ under hydrogen atmosphere at 300 C for 120 min, and then evacuated under high vacuum for 120 min. After that process, CO chemisorption experiments were performed at 30 C. The amount of irreversibly adsorbed CO was determined as the extrapolation of the difference between the total 2
uptake and the reversible uptake to zero pressure. Powder X-ray diffraction (XRD) of bimetallic catalysts was used to probe interaction between Re and Ru and to provide information regarding crystal phase. Powder diffraction was performed by Rigaku XRD diffraction meter (Rigaku D/Max- RB, Rigaku, Japan) using CuKα (λ=1.54178 Å) as the radiation source, operated at 40 kv and 100 ma with a scan speed of 8 min -1. Temperature-programmed reduction (TPR) analyses was performed on an AutoChem 2910 instrument (Quantachrome, USA) equipped with a thermal conductivity detector (TCD). Prior to the TPR analysis, the samples were firstly treated with inert gas for 1 h at 200 C, and cooled to ambient temperature under inert. The atmosphere were then changed to 10% H2/Ar and kept for 40 min. This treating procedure was then followed by a TPR analysis using 10% H2/Ar at a flow rate of 100 ml min -1 from room temperature to 800 C with a temperature ramping rate of 10 C min -1. Temperature-programmed desorption (TPD) were also carried out with the same equipment with TPR analyses, to study the ability of hydrogen adsorption and activation of Re-Ru/C bimetallic catalysts. The Re-Ru/C catalysts were loaded into the fritted quartz tube, pretreated at 300 C for 120 min under 10% H2/Ar atmosphere and afterwards cooled to 50 C under N2 atmosphere. H2 adsorption was performed at 50 C in 10% H2/Ar mixture with a flow rate of 100 ml (STP)/min. After H2 adsorption, the samples were purged with N2 for 120 min. After that, the H2 desorption was detected under N2 atmosphere with a temperature ramp at 10 C min -1 from 50 to 900 C. In our experiments, the peak area of TPD profiles was used for quantitative analysis. X-ray photoelectron spectroscopy (XPS) measurements were performed on an ESCALAB250 instrument (Thermo VG, USA). Monochromatic AlKa source (hν = 3
1486.6 ev) was used at a power of 150 W. The survey scans were collected for binding energy spanning from 800 to 0 ev. The pass energy was 50 ev with a step of 0.1 ev for high-resolution spectra. In the test, binding energies were referenced to C 1s (284.6 ev). The Ru 3p and Re 4f spectra were used to be invested in our experiments. Before the measurement, the samples were stored under same conditions and made sure that they were exposed to the air for same period of time. After that, these samples were analyzed by XPS simultaneously to reduce the experimental error to the maximum extent. Transmission electron microscopy (TEM) images were performed on a FEI Technai F20 electron microscope. The HAADF-STEM and corresponding elemental mapping were performed in STEM mode in combination with energy dispersive X-ray spectroscopy (EDX) using a DX4 analyzer system (EDAX) on a Philips CM200 FEG TEM electron microscope. The catalyst samples were pre-reduced by H2 under 300 C for 120 min before measurement and then dispersed in ethanol with ultrasound as soon as possible. The average diameter was calculated by measuring over 200 particles from various TEM images. Scanning electron microscopy (SEM) and elemental mapping were performed on a FEI QUANTA 450 electron microscope. The catalysts were loaded on carbon conductive tapes and tested in vacuum. 3. Kinetic Study 3.1 Assessing Transport Control in Aqueous Hydrogenation of SA Since the reaction occurred in a heterogeneous system (liquid-gas-solid), it is essential to consider the influence of external and internal transport for kinetic study in this experiment. 3.1.1 The Influence of External Diffusion 4
Given the uncertainty in estimating mass transfer coefficients, experimental analysis of external mass transport limitations is reasonable. For autoclave reactor, increasing stirring speed not only contribute to the mass transfer of SA, but also is benefit to the diffusion of H2 in aqueous solutions. Thus the hydrogenation of SA was carried out over different stirring speed (from 300 to 800 rpm) while maintain same other reaction conditions. We observed little increase in hydrogenation rate by increasing stirring rate when the stirring speed was above 700 rpm. This results reveal that external transfer of SA and H2 is sufficiently rapid such that it has a limited influence on the rate of hydrogenation. Because of that, 800 rpm was sufficient in this system to eliminate external diffusion effect as much as possible. 3.1.2 The Influence of Internal Diffusion The Thiele Modulus (φ) in equation 1 is often used to estimate the influence of internal diffusion on the reaction rate. φ= V p a p k v D e Here, V p is the volume of catalyst, a p is the exterior surface area of catalyst, k v is the reaction rate constant based on the volume of catalyst, D e is effective diffusion coefficient. In this experiment we measured TOFs over Re-Ru bimetallic catalysts with different particle size (<75 um, 75-100 um and 100-150 um) for SA hydrogenation when the reaction rate was sufficiently high at 180 C that internal diffusion is likely to control the reaction rate. The results showed that the TOFs has a slight fluctuations for these three particle sizes which showing that the internal diffusion didn t control the 5
observed reaction rate significantly when the particle size was below 150 um. The Thiele Modulus ( φ ) was far less than 0.4 for any reasonable effective diffusion coefficient when the particle size was less than 100 um, suggesting the influence of internal diffusion could be ignored. Thus all catalysts in this experiment were sieved to make sure that the particle size is less than 75 um. 3.2 The Fitting of Data In this manuscript, the apparent reaction order and reaction rate constants over Re/C and ReRu/C were calculated with the data in Fig. S2-S4. Fig. S2-S4 shows the time course of SA hydrogenation or GBL hydrogenation over ReRu/C and Re/C at different reaction conditions. In these figures, the plot are the raw data and the solid line denote the fitting results. In this experiments, the reaction orders for SA hydrogenation were simulated by Matlab according to the concentration curve in Fig. S2(A) and (B). During the fitting process, different initial value of reaction order was input to Matlab program and then the results of model predictions at different temperature were obtained. The apparent reaction order is most reasonable when the results of model predictions exhibit highest degree of correlation. Meanwhile, the reasonable reaction rate constants were also obtained through the fitting of data. After that, apparent activation energy was calculated on the basis of reaction rate constants with Origin and the degree of correlation will examine the above fitting results. Then, the reaction rate constants for ReRu/C under different pressure can be calculated by using the reaction order of SA. The apparent reaction order for hydrogen pressure can be obtained with the reaction rate constants under different pressure as shown in Fig. 7(A). The reaction orders and apparent activation energy for GBL hydrogenation were calculated with the same method as provided above. 6
Tables and Figures Table S1. XPS analyses results of Re-Ru/C bimetallic catalysts Re 4f (%) Ru 3p (%) Catalysts Re 0 Re 4+ Re 6+ Ru 0 Ru 4+ Re/C 7.5 20.3 72.2 - - Re3Ru/C 9.2 10.6 80.2 49.3 50.7 ReRu/C 18.2 19.2 62.6 54.0 46.0 ReRu3/C 12.0 13.2 74.8 50.0 50.0 Ru/C - - - 52.6 47.4 7
Table S2. H2-TPD analyses results of Re-Ru/C bimetallic catalysts Relative adsorption quantity Catalysts PeakⅠ Peak Ⅱ Peak Ⅲ Total Re/C 1.0 3.0 3.7 7.7 Re3Ru/C 0.6 1.4 6.5 8.5 ReRu/C 1.3 5.3 2.4 9.0 ReRu3/C 2.1 2.9 3.9 8.9 Ru/C 3.4 3.8 2.0 9.2 8
Table S3. Hydrogenation of intermediates over Re-Ru/C bimetallic catalysts. Yield (%) Substrate Catalysts GBL BDO THF NBA NPA BA PA GBL BDO BA PA Re/C 4.7 8.1 0.4 0.1 ReRu/C 29.4 28.7 5.0 8.9 Ru/C 0.9 1.6 0.2 2.5 2.1 16.1 Re/C 2.8 20.4 0.7 0.09 ReRu/C 3.7 16.2 9.4 18.8 Ru/C 1.4 13.8 0.8 24.1 0.6 Re/C 16.0 ReRu/C 52.3 Ru/C 1.9 Re/C 15.3 ReRu/C 50.2 Ru/C 1.8 Reaction conditions: 200 C, 8.0 MPa, 0.1 g catalysts, 20 g solutions (10 wt.%), 6 h. 9
Table S4. The influence of impurities on catalytic activity of ReRu/C catalysts. Substrate Con.SA (%) Sel. (%) GBL BDO THF NBA NPA Acetic acid 99 37.3 31.6 17.3 7.5 6.5 Pyruvic acid 91 51.0 16.9 15.9 7.4 8.8 Reaction conditions: 180 C, 8.0 MPa, 20 g solutions (10 wt.% SA, 1 wt.% Impurities), 0.2 g catalysts, 10 h. 10
Scheme S2. Proposed reaction mechanism of SA hydrogenation over Ru/C catalyst. 11
Scheme S3. Proposed reaction mechanism of SA hydrogenation over Re/C and ReRu/C catalysts, which is focusing on the combined effect of Re and Ru. Step 1 is fast and Step 2 is slow when M equals to ReRu; Step 1 is slow and Step 2 is fast when M equals to Re. 12
Fig. S1. XRD patterns of Re-Ru/C bimetallic catalysts. 13
Fig. S2. Time course of SA hydrogenation over ReRu/C and Re/C at different temperature (A and B) and pressure (C) (the correlation coefficient R 2 >0.99). The plot is raw data and the solid line is fitting result. Reaction conditions: (A) 0.2 g catalysts for 180-220 C; (B) 0.1 g catalysts for 160, 170, 180 C and 0.05 g catalysts for 190, 200 C; (C) 0.1 g catalysts for 5.0-8.0 MPa and 0.03 g catalysts for 9.0 MPa. 14
Fig. S3. Time course of GBL hydrogenation over ReRu/C at different temperature (the correlation coefficient R 2 for GBL is above 0.99, the correlation coefficient R 2 for BDO is above 0.99, the correlation coefficient R 2 for THF is above 0.98). The plot is raw data and the solid line is fitting result. Reaction conditions: 0.1 g catalysts for 140, 150, 160 C and 0.05 g catalysts for 170, 180 C. 15
Fig. S4. Time course of GBL hydrogenation over Re/C at different temperature (the correlation coefficient R 2 for GBL is above 0.99, the correlation coefficient R 2 for BDO is above 0.99, the correlation coefficient R 2 for THF is above 0.98). The plot is raw data and the solid line is fitting result. Reaction conditions: 0.3 g catalysts for 140, 150, 160, 170 C and 0.2 g catalysts for 180 C. 16
Fig. S5. Products distribution for aqueous hydrogenation of SA over ReRu/C catalyst at different temperature. Reaction conditions: 8.0 MPa, 20 g solutions (10 wt.% SA), 0.2 g catalysts. 17
Fig. S6. Aqueous hydrogenation of succinic acid over ReRu/C catalysts with respect to recycle run. Reaction conditions: 180 C, 8.0 MPa, 20 g solutions (10 wt.% SA), 0.2 g catalysts, 6 h. 18