The effect of modifying Pd/Al2O3 catalysts by atomic layer deposition of 1 nm ZrO2 films was studied. For deposition on oxidized, PdO/Al2O3 catalysts, TEM imaging, EDS mapping, and metal-dispersion measurements confirmed the presence of the thin ZrO2 over both the Al2O3 support and the metal particles. The ZrO2 films were surprisingly stable, forming a well-crystallized phase only above 1173 K. The ZrO2 coating over the PdO particles created a semicore–shell-like structure that stabilized the metal against sintering in air at 1073 K. Steady-state, methane oxidation rates on unmodified PdO/Al2O3 decreased with increasing catalyst calcination temperature, but rates on the ZrO2-covered surfaces increased with increasing calcination temperature.

The three-phase hydrodeoxygenation reaction of 5-hydroxymethylfurfural (HMF) with H 2 was studied over a 10 wt % Pt/C catalyst using both batch and flow reactors, with ethanol, 1-propanol, and toluene solvents. The reaction is shown to be sequential, with HMF reacting first to furfuryl ethers and other partially hydrogenated products. These intermediate products then form dimethyl furan (DMF), which in turn reacts further to undesired products. Furfuryl ethers were found to react to DMF much faster than HMF, explaining the higher reactivity of HMF when alcohol solvents were used. With the optimal residence time, it was possible to achieve yields approaching 70% in the flow reactor with the Pt/C catalyst. Much higher selectivities and yields were obtained in the flow reactor than in the batch reactor because side products are formed sequentially, rather than in parallel, demonstrating the importance of choosing the correct type of reactor in catalyst screening.

The three-phase hydrodeoxygenation (HDO) of 5-hydroxymethylfurfural (HMF) and hydrogenation of 2,5-dimethylfuran (DMF) were studied over six carbon-supported metal catalysts (Pt, Pd, Ir, Ru, Ni, and Co) using a tubular flow reactor with 1-propanol solvent, at 180°C and 33 bar. By varying the space time in the reactor, the reaction of HMF is shown to be sequential, with HMF reacting first to furfuryl ethers and other partially hydrogenated products, which then form 2,5-dimethylfuran (DMF). Ring-opened products and 2,5dimethyltetrahydrofuran (DMTHF) were produced only from reaction of DMF. Rate constants for the pseudo-first-order sequential reactions were obtained for each of the metals. The selectivities for the reaction of DMF varied with the metal catalyst, with Pd forming primarily DMTHF, Ir forming a mixture of DMTHF and open-ring products, and the other metals forming primarily open-ring products. Catalyst stabilities followed the order Pt ~ Ir > Pd > Ni> Co > Ru. Since the stability order correlated with carbon balances in the product (>93% for Pt; <75% for Ru), deactivation appears to be caused by deposition of humins on the catalyst.

a b s t r a c tThe adsorption and reaction of anisole on Pt and PtZn catalysts were investigated using both model single crystal and high surface area supported metal catalysts. Temperature programmed desorption (TPD) and high resolution electron energy loss spectroscopy (HREELS) studies of the interaction of anisole with Pt (1 1 1) demonstrated that there is a strong interaction between the phenyl ring of anisole and the surface, resulting in CAO and CAH bond scission at relatively low temperatures. In contrast, anisole was observed to bond to a Zn-modified Pt(1 1 1) surface primarily via the oxygen at Zn sites or possibly adjacent Pt sites, with the phenyl ring tilted away from the surface. Such bonding configuration facilitated selective CAO bond cleavage producing phenyl groups and methoxide groups with the latter being bonded to the Zn sites. These results suggested that PtZn may be an effective catalyst for hydrodeoxygenation (HDO) of lignin-derived aromatic oxygenates with low activity for ring hydrogenation. This hypothesis was then tested and verified by investigating the reaction of anisole and H 2 over high surface area carbonsupported Pt and PtZn catalysts.

Al 2 O 3 powders were modified by Atomic Layer Deposition (ALD) of CeO 2 to produce composite catalyst supports for Pd. The weight of the support was found to increase linearly with the number of ALD cycles. This, together with TEM images, indicated that the CeO 2 grows as a dense, conformal film, with a growth rate of 0.02 nm per cycle. The films showed good thermal stability under oxidizing conditions. XRD measurements on a sample with 0.28 g CeO 2 /g Al 2 O 3 showed no evidence for crystalline CeO 2 until calcination above 1073 K. Water-gas-shift rates on 1-wt% Pd catalysts supported on the CeO 2 ALD-modified Al 2 O 3 were essentially identical to rates on conventional Pd-CeO 2 catalysts and much higher than rates on a catalyst in which Pd was supported on Al 2 O 3 with CeO 2 added by infiltration. The WGS rates, together with results from FTIR and COO 2 pulse studies, suggest that all of the Pd is in contact with CeO 2 on the ALD-prepared supports and that it should be possible to prepare high-surface-area, functional supports using ALD.

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High-surface-area iron oxides were prepared by Atomic Layer Deposition (ALD) on 130m 2 /g γ-Al 2 O 3 for use as a catalyst support. Measurements of the sample mass, surface area, and pore-size distribution as a function of the number of ferrocene-O 2 ALD cycles at 623 K suggested that the iron oxide grew as a dense, conformal film with a growth rate similar to 0.016-nm per cycle. While films with 20 ALD cycles (20Fe 2 O 3-Al 2 O 3 , 0.25 g Fe 2 O 3 /g Al 2 O 3) were difficult to distinguish by HAADF STEM, EDS mapping indicated the Al 2 O 3 was uniformly coated. Raman Spectroscopy showed the films were in the form of Fe 2 O 3 ; but XRD measurements on samples with as many as 100 ALD cycles (100Fe 2 O 3-Al 2 O 3 , 0.84 g Fe 2 O 3 /g Al 2 O 3) showed no evidence for crystalline iron-oxide phases, even after calcination at 1073 K. Specific rates for the water-gas-shift (WGS) reaction on the ALD-coated samples were significantly lower than those on bulk Fe 2 O 3. However, addition of 1 wt.% Pd to Fe 2 O 3 /Al 2 O 3 supports prepared by ALD exhibited specific rates that were much higher than that observed when 1 wt.% Pd was added to Fe 2 O 3 /Al 2 O 3 prepared by conventional impregnation of Fe salts, suggesting more uniform contact between the Pd and FeO x phases on samples prepared by ALD.