Date of Award

2018

Document Type

Open Access Dissertation

Department

Chemical Engineering

First Advisor

Christopher Williams

Abstract

Heterogeneous catalytic hydrodeoxygenation (HDO) of biomass-derived feeds is a deoxygenation process that is of highly interest. Carboxylic acids are one of the main components of bio-oils and acetic acid is one of the most abundant of these carboxylic acids. This acid is rich in oxygen, therefore a lot of research to produce fuel and other valuable chemicals such as ethanol is of interest.

This dissertation explores the gas-phase catalytic HDO of AA over catalysts supported on activated carbon (Cp-97). Temperature-dependent conversion and selectivity were studied at 1 atm from 200-4000C with an AA concentration of 1.1% and 20% H2 balanced in He. The first part of this work focuses on commercial catalysts: 5%Pt, 5%Pd, 5%Ru and 5%Rh supported on Cp-97. For Pt, Pd and Rh the main pathway at low temperature was decarbonylation (200-3000C) and at higher temperatures (350-4000C) the main pathways were decarbonylation/decarboxylation and ketonization. However, for Ru at low temperatures (200-2500C) the main pathway was decarboxylation, and at high temperature (300-4000C), the main pathway was decarbonylation. The activity trend based on TOF at 2000C was found to follow: Ru > Rh~Pt > Pd. The activities of all catalysts at 2000C were found to decrease after reaction at 4000C and returning to 2000C. This is attributed to coking. The reaction orders in AA and H2 measured at 2000C for all catalysts are generally well below ~0.5, suggesting relatively strong adsorption of both reactants on all metal surfaces. The temperature-dependence of the reaction rates were examined over the range 200-240 0C having apparent activation energy values of around 20-23 kcal/mol.

The second project studies the HDO of AA at the same conditions, but adding Sn as a second metal on Pt and Ru (SnPt, Sn2Pt, SnRu and Sn2Ru) using incipient wetness. The selectivity for SnPt and Sn2Pt goes towards ethanol and for SnRu and Sn2Ru goes mainly towards acetaldehyde from 200-3000C, therefore at lower temperature the main path way is hydrogenation. At higher temperatures (350-400 0C) the main pathways are hydrogenation and decarbonylation and ketonization. For the Pt-based catalysts, a bifunctional and geometrical effect were found and for Rubased catalyst a strong electronic and bifunctional effect were deduced from XPS. The activity at 2000C based on TOF was as follow: Sn2Ru>SnPt~Sn2Pt~SnRu. The reaction order for AA were bellow ~0.5 for all catalyst and the reaction order for H2 was low as well for the Pt-based catalysts. However, the reaction order for SnRu and Sn2Ru was ~1. The apparent activation energy for the catalyst were in the range of 13-20 kcal/mol.

Finally, on a different project phosphorous nickel phosphide (Ni2P) is investigated. This material is being used in the HDO reaction of different carboxylic acids. The focus of this work is to investigate (P) diffusion in bulk Ni2P by density functional theory (DFT) to find the origin of the low temperature P diffusion into the surface. The Ni2P bulk structure consists of two types of layers, Ni3P2 and Ni3P stacked along the [0001] direction. Two types of P vacancies in Ni2P were studied: VP1 (P deficient in Ni3P2), and VP2 (P deficient in Ni3P). VP1 was a somewhat more stable point defect than VP2 by 0.20 eV. The P diffusions to vacancies (VP1 and VP2 ) had large diffusion barriers of more than 1 eV, except the P diffusion path along [0001] direction through an interstitial site in Ni3P (IP 1!2) and then to VP1 , which showed the lowest energy barrier of about 0.18 eV. The DFT calculations suggested that the two adjacent vacancies (both VP1 ) allow the local rearrangement of the structure to form a tetrahedral structure at the intermediate state. We have proposed a new diffusion mechanism in the intermetallic compound named interstitial-vacancy diffusion mechanism.

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