**2.2. Catalyst preparation**

*Catalyst precursor synthesis*. All catalyst precursors were prepared by the precipitation-deposition method. **Figure 1** shows a schematic of the experimental setup for catalyst precursor synthesis.

**Table 3** lists catalyst precursor samples designation, synthesis operating parameters and nickel loadings.

The details of the synthesis procedures for differently supported nickel-based catalyst precursors were given in our earlier works [29, 69, 57, 31].

*Catalyst precursor reduction*. The reduction of the catalyst precursors was performed by a dry reduction method in a laboratory apparatus shown in **Figure 2** (line: reduction). Catalyst precursors were heated up to 430°C at a rate of 1.5°C min−1 under flowing H<sup>2</sup> /N2 gas mixture (150 cm<sup>3</sup> min−1, 50 vol% of H<sup>2</sup> ) and maintained at 430°C for 5 h. Precursor treated in this way is referred to as Rp (e.g., (Ni-Mg/D)Rp).

**Figure 1.** Schematic representation of the experimental setup—catalyst precursor synthesis.


\*Referred to catalyst precursors sample prepared from nitrate salts of nickel and modifier.

a Symbols in sample designation: A—acetate, C—chloride, F—formate, S—sulfamate; numbers refer to the Ag loading: 0.16 wt% of Ag (Ni-Mg-Ag0.16/D), 1.55 wt% of Ag (Ni-Mg-Ag1.55/D), 5.88 wt% of Ag (Ni-Mg-Ag5.88/D); Ni/Ag0.16 (atomic ratio) = 400/1, Ni/Ag1.55 (atomic ratio) = 40/1, Ni/Ag5.88 (atomic ratio) = 10/1.

b Constant parameters: TPD—reaction temperature (precipitation-deposition), tAG—aged temperature, precipitant: anhydrous Na2 CO3 approx. 50% in excess with respect to a sum of Ni and Mg molar content.

**Table 3.** Catalyst precursor systems and samples prepared.

*Reduced catalyst precursor soaking—final catalyst*. After cooling down to room temperature, reduced catalyst precursors were protected by soaking in pure paraffin oil. After removing the excess of paraffin oil by filtering, the final catalyst was stored.

*Reduced catalyst precursor passivation*. Passivation of the reduced catalyst precursors was necessary to prevent the exceptional pyrophoricity of the metallic nickel before the reduced precursor was exposed to air for characterization and handling. This treatment was carried out in a laboratory apparatus depicted in **Figure 2** (line: passivation). Reduced catalyst precursor was passivated at room temperature in a N2 stream (150 cm<sup>3</sup> min−1) containing 350 ppm O<sup>2</sup> for 30 min.

#### **2.3. Characterization**

Analytical grade chemicals and pure hydrogen (99.999%) and nitrogen (99.999%) were employed in the experiments and none of these gases contained catalyst-poisoning sub-

*Catalyst precursor synthesis*. All catalyst precursors were prepared by the precipitation-deposition method. **Figure 1** shows a schematic of the experimental setup for catalyst precursor synthesis. **Table 3** lists catalyst precursor samples designation, synthesis operating parameters and

The details of the synthesis procedures for differently supported nickel-based catalyst precur-

*Catalyst precursor reduction*. The reduction of the catalyst precursors was performed by a dry reduction method in a laboratory apparatus shown in **Figure 2** (line: reduction). Catalyst

) and maintained at 430°C for 5 h. Precursor treated in this way

/N2

gas mixture

precursors were heated up to 430°C at a rate of 1.5°C min−1 under flowing H<sup>2</sup>

**Figure 1.** Schematic representation of the experimental setup—catalyst precursor synthesis.

stances such as oxygen or sulfur.

sors were given in our earlier works [29, 69, 57, 31].

136 New Advances in Hydrogenation Processes - Fundamentals and Applications

min−1, 50 vol% of H<sup>2</sup>

is referred to as Rp (e.g., (Ni-Mg/D)Rp).

**2.2. Catalyst preparation**

nickel loadings.

(150 cm<sup>3</sup>

*Chemical analyses*. The chemical analysis of nickel (Ni) was performed by standard test methods for quantitative analysis (dimethylglyoxime method). The silver (Ag) loading was determined using inductively coupled plasma-optical emission spectroscopy (ICP-OES) on an iCAP 6500 Duo apparatus (Thermo Fisher Scientific). Before the analysis, the precursors were subjected to microwave digestion using a Milestone Ethos 1 advanced microwave digestion system.

*Nitrogen physisorption (N2 -physisorption)*. N2 adsorption/desorption isotherms of the catalyst precursors at −196°C were measured on a Thermo Finnigan Sorptomatic 1990. Precursors

**Figure 2.** Schematic representation of the experimental setup—catalyst precursor reduction/passivation.

were previously degassed for 16 h at 110°C and 10−3 Torr (1 Torr = 133.3 Pa). The BET equation was used to calculate the specific surface area, *S*BET. Total pore volume, *V*p, was estimated at a relative pressure of 0.99.

*Mercury porosimetry (Hg-porosimetry)*. Hg-porosimetry measurements were performed in the fully automated conventional porosimeters: 1. Thermo Scientific Pascal 140 porosimeter (pressure range: 0.01–0.1(0.4) MPa; pore size (diameter) range: 3.8–116 μm); 2. Thermo Scientific Pascal 440 porosimeter—Solid 1.3.4 software (pressure range: 0.1–400 MPa; pore size (diameter) range: 0.0036–15 μm)—data acquisition with the software package Solid 1.3.4; 3. Carlo Erba Macropore 120 porosimeter (pressure range: 0.01–0.1 MPa; pore size (diameter) range: 3.8–116 μm (or 15–150 μm); 4. Carlo Erba 2000 porosimeter (pressure range: 0.1–200 MPa; pore size (diameter) range: 0.0075–15 μm)—data acquisition with the software package Milestone 200.

*Density measurements*. Apparent densities were measured using a helium pycnometer, which uses a gas displacement technique to determine the volume of the solid material under test. The measurements were performed using a Pycnomatic ATC (Thermo Fisher Scientific).

*IR measurements*. IR spectra were recorded on a Perkin Elmer 983 G spectrometer (4000–250 cm−1) and a Thermo Scientific Fourier transform Nicolet 6700 spectrometer (4000–400 cm−1). KBr pellet method was used: 1 mg of precursor was well mixed into 200 mg fine KBr powder and the finely pulverized and put into a pellet-forming die.

*X-ray diffraction (XRD)*. Powder XRD patterns were obtained with a Siemens D5005 diffractometer, equipped with a graphite monochromator and Antoan Paar chamber. Copper filtered Cu Kα radiation (λ = 0.154184 nm) was employed covering 2*θ* angles from 5 to 80° or from 10 to 100°. The average metal crystallite sizes were estimated by application of the Sherrer equation. The width of the Ni-(111) peak at half-maximum was corrected for Kα doublet and instrumental broadening.

*Hydrogen temperature programmed reduction (H2 -TPR)*. Hydrogen temperature programmed reduction experiments were carried out in an automatic apparatus Thermo Scientific TPDRO, Pulse Chemisorb 1100. H<sup>2</sup> -TPR experiments of catalyst precursors were performed in the temperature range 50-900°C, using a flow of H<sup>2</sup> /Ar (20 cm<sup>3</sup> min−1, 4.9 vol% of H<sup>2</sup> ) and a heating rate of 2°C min−1. A cooling trap filled with 3A-MS was installed between the oven and TCD to remove the water formed during the reduction. The consumption of H2 was monitored by a thermal conductivity detector. The detector response was calibrated by reducing a known mass of CuO. TPR profiles were normalized to the same mass of catalyst precursors.

*Hydrogen chemisorption (H2 -chemisorption)*. H2 -chemisorption data were obtained using both the static method (standard volumetric apparatus) and the dynamic method (Thermo Scientific TPDRO, Pulse Chemisorb 1100).

*Experimental setup—standard volumetric apparatus. In situ* reduction of catalyst precursors at 430°C for 1 h by passing a mixture of hydrogen and nitrogen (H<sup>2</sup> /N2 = 1:1 v/v) over the sample. Reduction conditions were as follows: heating rate: 2°C min−1 and H2 /N2 gas mixture flow of 20 cm<sup>3</sup> min−1. After reduction, the precursors were degassed at 10−4 Pa for 4 h at the same temperature and cooled at 25°C to carry out chemisorption measurements. The pressure range of the isotherms was 0.1–13.3 kPa and the amounts of hydrogen chemisorbed were calculated by

**Figure 2.** Schematic representation of the experimental setup—catalyst precursor reduction/passivation.

138 New Advances in Hydrogenation Processes - Fundamentals and Applications

extrapolation of the isotherms to zero pressure. Further details about the expressions used to calculate nickel crystallite sizes can be found in our previous paper (see [29]).

*Experimental setup—pulse chemisorb TPDRO 1100. In situ* reduction of catalyst precursors at 430°C (2°C min−1) for 1 h, under a flow of 20 cm3 min−1 H2 /Ar (4.9 vol% of H<sup>2</sup> ). After reduction, the precursors were degassed by temperature programmed desorption at 425°C (carrier gas Ar) and cooled at 45°C, to carry out chemisorption of H<sup>2</sup> . Finally, the catalyst precursors were subjected to a known number of calibrated pulses (0.353 cm3 ) of pure H2 at 45°C.

*X-ray photoelectron spectroscopy (XPS)*. The quantitative chemical composition of surfaces of catalyst precursors and the valence state of studied ions were obtained by X-ray photoelectron spectroscopy. XPS measurements were performed using a VG Scientific Escalab Mk II spectrometer interfaced with the necessary data handling software Lab Cal 2. Spectra were recorded under ultrahigh vacuum conditions (10−8 Torr), using Al Kα primary radiation (1486.6 eV). Data were collected in the sequence of a survey scan (to determine the C 1s reference), followed by scans of the O 1s, S 2p, Ni 2p3/2 and Ag 3d regions to minimize the time of exposure to X-rays.
