Fig. 1b shows the FF hydrogenation performances over the Cu/SiO
2, Cu/SiO
2-FD and reference commercial catalysts. The selectivity to FA is nearly 100% in all cases. The Cu/SiO
2-FD exhibits higher FA yield at 80 ℃, 100 ℃ and 120 ℃ compared to Cu/SiO
2. And the activity of Cu/SiO
2-FD is much higher than that of commercial CuCr-S catalyst and CuSi-C catalyst. For the commercial CuSi-C catalyst on the equal copper amount of Cu/SiO
2-FD, its performance as that marked as CuSi-C-2 is considerably far inferior to that of the Cu/SiO
2-FD. Take the Cu/SiO
2 and Cu/SiO
2-FD for comparison (
Fig. 1c), FA yield increases with the increasing of reaction time, the Cu/SiO
2-FD performs better than Cu/SiO
2 in all cases. The performance of Cu/SiO
2-FD catalyst is also superior to majority of the copper based catalysts that were reported previously (Table S1 in Supporting information). And the composition of the Cu/SiO
2-FD is much simpler compared to the reference catalysts summarized in Table S1. The stability of the Cu/SiO
2-FD was further assessed using a trickle bed reactor in continuous mode, and the result is depicted in
Fig. 1d. There is no obvious decrease of FF conversion and FA selectivity during the whole reaction (~550 h). The above results demonstrate that the silica supported copper catalyst prepared by ammonia evaporation using freeze drying as drying technology (Cu/SiO
2-FD) is more active than that of the silica supported copper catalyst synthesized by ammonia evaporation using conventional oven drying (Cu/SiO
2), commercial CuCr-S catalyst and commercial CuSi-C catalyst supplied by a FA plant. And the Cu/SiO
2-FD catalyst shows excellent stability. Therefore, the freeze drying promotes the performance of silica supported copper catalyst for FF hydrogenation in liquid phase.